(FORTUNE Magazine) – YOU'VE BEEN X-rayed, CAT-scanned, poked, prodded, and palpated in all the most embarrassing places. Now a kindly professional you've never met is about to pull up a folder with your name on it and tell you what he or she found. Only it's not your lower intestine that's about to be discussed but something even more personal: you. Your personality. The way you deal with people. Your talents, your values, your ethics, your leadership. And the folks who did the poking and temperature taking weren't anonymous technicians but a half dozen or more of your closest colleagues at work. You, pal, are about to be stripped naked by an increasingly popular human- resources device aimed at improving your on-the-job performance: feedback from co-workers -- also known as 360-degree feedback and multi-rater assessment. Here's how it works. Everyone from the office screwup to your boss, including your crackerjack assistant and your rival across the hall, will fill out lengthy, anonymous questionnaires about you. You'll complete one too. Are you crisp, clear, and articulate? Abrasive? Spreading yourself too thin? Trustworthy? Off-the-cuff remarks may be gathered too. A week or two later you'll get the results, all crunched and graphed by a computer. Ideally, all this will be explained by someone from your human-resources department or the company that handled the questionnaires, a person who can break bad news gently. You get to see how your opinion of yourself differs from those of the group of subordinates who participated, your peer group, and the boss. The results won't necessarily determine your pay, promotions, or termination. At least, not yet. The technique as it's now applied doesn't work well for that. When it is designed to provide information that you can use to become a better manager, scores from your handpicked pals or from randomly chosen associates typically turn out remarkably similar. But when used as the basis for formal performance evaluations, things change. Friends pump up your | score, rivals become remarkably lukewarm, and that staff boob you keep reaming out cuts you dead. Mark Edwards, president of Teams Inc., a feedback company in Arizona, says he doesn't know of any major company that relies primarily on 360-degree feedback for evaluations. But his firm is working on ways to weed out slanted responses, and he says lots of clients are intrigued by the idea of using feedback for appraisals. Even if it doesn't find its way into your personnel file, make-you-better feedback can still hurt. Though it often contains pleasant news, feedback can be surprising, powerful, and uncomfortable stuff, as conversations with a dozen feedback recipients -- ranging from corporate CEOs and division managers to second-tier supervisors -- reveal. What probably wounds deepest are bad reports about interpersonal skills. If your buddies think you're lousy at budgeting, no huge deal. But several feedback experts singled out "untrustworthy" as the most devastating single criticism for most people. "Bad listener" stings. Word that your judgment and thinking are subpar will rattle almost anyone too, says Susan Gebelein, a vice president at Personnel Decisions Inc., a big human-resources consulting company in Minneapolis. "Those are core competencies," she says. What's most interesting about feedback isn't the pain it causes, the mechanics of its operation, or its growing popularity. It is the huge variety of unpredictable comments -- and potential learning -- that it delivers. Most people are surprised by what they hear. Only a fraction of managers have a good grasp of their own abilities. Those with certain kinds of blind spots are routinely judged less effective by co-workers. One boss thought he was a fabulous writer. His underlings suffered in silence as he routinely criticized their reports and corrected their grammar, but they never mentioned their discomfort to one another. At feedback time, they all mentioned that they thought he was a mediocre writer and wished he would quit bothering them. He was supremely embarrassed, apologized, and stopped. The president of Raychem, a $1.5 billion electronics and electrical equipment company in California, says he didn't get any major surprises about himself but he was intrigued to learn that he wasn't fooling his subordinates either. They told Robert Saldich he wasn't good at contingency planning. His reaction: "Shucks. I haven't been hiding here." One manager learned that he had two annoying traits, recalls consultant Edwards: He stood too close to people, and little bits of spit flew from his mouth when he spoke. A very bad combination. He began keeping his distance and got speech therapy, and his career prospects improved dramatically. Joe Malik, manager of a team of engineers at AT&T, got nicked for his vigorous temper. That was not a big revelation -- he was already working on correcting it. But he was startled to learn that when his direct reports asked him about the company's plans for the group, he often scrunched up in his chair. His subordinates thought he was being evasive. "I was just trying to come up with the answer," he says. "If I were being evasive, I would have said I couldn't answer."

MOST REVEALING to Malik was that his subordinates expected things of him he'd never imagined. "I found out I need to articulate the vision and mission of our little unit. I was surprised. Not because I prided myself on my visioning, but because we're a heads-down organization working on networking products for the phone system. But people want to know where we're going and whether the managers' heads are screwed on right, and what I aspire the business to be." There are plenty of all-too-common complaints and familiar patterns that surface in feedback too. Many companies are using feedback for cultural change, to accelerate the shift to teamwork and employee empowerment. Bosses who charged up the corporate ladder by controlling everything and barking like a drill sergeant often get an earful from eagerly critical underlings. Kim Jeffery, the CEO of Nestle's Perrier operation in the U.S., didn't need feedback to know he was a demanding manager. It had been his style on purpose. "Our company style resembled the lion-tamer school of management," he says, referring to relations among top executives. "You keep them all on their own platforms and deal with them as individuals. Because if you don't, they'll kill each other and the lion tamer." The technique had worked for his predecessor, but after a year and a half on the job, Jeffery realized that he needed a new style. "The company was growing and maturing. And I wasn't getting the kind of input from managers I needed to make good decisions." He brought in Alex Platt, a Connecticut psychologist who works with business leaders, to handle feedback questionnaires and conduct interviews with senior executives. Jeffery's subordinates revealed that his elevation to the presidency had | made him a far more frightening figure to them than he'd been before. His temper and occasional "public whippings" of senior managers were tolerable when he was head of sales and marketing but terrifying when he had the ultimate authority to fire anybody. He was amazed. He had grown up in modest circumstances and disdained the pomp and ceremony he associated with many top execs. "I thought I was seen as a regular guy," he says. "I didn't realize the impact of my words on people." Some managers told him that they were so intimidated, they weren't coming to him with problems and ideas. "I was mad at myself when I heard," Jeffery says. "I know the right way to do things." He says he's better now -- fewer outbursts and more effort to get managers working together -- but not perfect. "With one or two lapses, I'm told I've done very well." Jerry Wallace, an up-and-coming manager at General Motors, was surprised by his feedback too. "There were a couple of 'wows,'" says Wallace, who recently became head of personnel at a Saturn assembly plant in Tennessee. He discovered he isn't nearly as flexible as he thought. His subordinates said they were frustrated because he sometimes made them follow prescribed processes without finding out whether there were better ways of doing things. "I was sure I was very flexible," he says. But the message that hit Wallace hardest was a common one: excess control. "The strongest message I got was that I need to delegate more," he says. "I thought I'd been doing it. But I need to do it more and sooner. My people are saying, 'Turn me loose.' "

FOR SOME control freaks, it takes massive doses of feedback before the lights finally come on. The Center for Creative Leadership, a nonprofit research center in Greensboro, North Carolina, puts on week-long feedback programs. In addition to getting questionnaire results from co-workers back home, 20 participants eyeball one another during simulated exercises and deliver unvarnished opinions about what they see. Wallace, who participated last August, says another manager at CCL finally saw how domineering he was and painfully realized the consequences. "He said, 'No wonder nobody wants to be on a team with me, and why I have to do everything myself.'" Okay, so you're into control, but everybody knows that you're only a curmudgeon on the outside, that you really have a warm, fuzzy spot in your heart for everyone. You might be that way, but don't be too sure everybody --or even anybody -- knows. Marc Breslawsky, head of the 8,000-employee office systems division at Pitney Bowes, didn't expect much from the feedback process, but he was curious about what employees thought of him. He found out that they viewed him as a man with little warmth who made cold, hard business decisions. "I assumed they knew I was pleased," he says. "I didn't pat people on the back. I didn't say thank-you. That wasn't my style. And if I had something difficult to discuss with someone, I didn't temper it by discussing their good parts. They felt I didn't care about them." His behavior, unfortunately, was infectious. "A lot of people saw me like that, and they treated their people that way." Now he's virtually a poster boy for feedback. "I started telling people what they do well and being more open in my discussions, and the results have been amazing." Teamwork is up, he says, and the time it takes to develop new products has been cut in half. Like many top bananas who experience big benefits from feedback, he wants his managers to go through the process too. Similar news awaited Donald Boudreau, an executive vice president in charge of branch banking at Chase Manhattan Bank. Disciplined, demanding, smart, sometimes intimidating, not a back patter. Most surprising of all: "Almost universally, people said I didn't have a sense of humor." He disagrees, but understands why people might think that: "I have one, but apparently I hide it." Any doubts about the accuracy of the feedback were dispelled when Boudreau asked his wife what she thought. Ouch. "She said they got it right." He approached subordinates and asked for help. They told him to back off a bit. "If I wanted people to discuss ideas with me without feeling they were getting a personal evaluation, I had to change." He doesn't crack bawdy limericks to warm things up at staff meetings now and doesn't sound as if he ever will. But when he criticizes a subordinate for poor performance, he tries to go back "and make sure the person doesn't see it as career terminating." Both Breslawsky at Pitney Bowes and Boudreau at Chase got some special insight from peers. Boudreau learned that taking a strong position in a meeting with peers and a boss can get under the skin of the peers. They understood that such a stance can often be appropriate advocacy, he says, but that "sometimes it looks like you're running for office." Breslawsky's feedback was even more pointed. Says he: "They said sometimes I seem to be shooting at them." How do managers rate themselves? Only about a third produce self-assessments that generally match what co-workers concluded. Another third -- called "high self-raters" -- have an inflated view of their talents, says Ellen Van Velsor, a researcher at the Center for Creative Leadership. The remaining third rate themselves lower than co-workers do. An oversize ego, it turns out, is murder in a manager. Almost invariably, the high self-raters are judged the least effective by co-workers, says Van Velsor. And yet, for reasons she can't entirely explain, high self-raters are more common high up in organizations than down low. "It could be that the higher they go, the less feedback they get, so their view of themselves gets distorted. Maybe they're being judged by a higher standard. And maybe they're just more self-confident than managers who don't reach senior positions."

Van Velsor says that on effectiveness, the self-doubters actually get better scores from co-workers than do the other two groups. She figures they probably work harder and rely more on others. But Paul Connolly, president of Performance Programs Inc., a feedback firm in Connecticut, thinks the strongest managers are the ones who size themselves up about right. Says he: "People with a good sense of their influence and effectiveness will use it to their advantage. The ones with the low self-image make people scurry around and waste a lot of effort." Clearly, feedback is not a panacea. Whether it permanently improves the managerial and leadership ability of those who get it is hard to pin down. Even Walter Ulmer, retiring president of CCL, agrees that measuring its effectiveness is difficult. William J. Miller, a research supervisor at Du Pont, helped install a feedback process for 80 scientists and support people several years ago. "A high or low score didn't predict a scientist's ability to invent Teflon," says Miller. "But what feedback did was really improve the ability of people to work in teams. Their regard for others, and behaviors that were damaging and self-centered, are what changed." Says Gebelein at Personnel Decisions: "Feedback delivers its wallop and generates changes depending on what a person and the organization value. If they care about relationships with others, it will have an effect in that area. If they emphasize management planning, it will have an impact there."

A FEW CONDITIONS are crucial for feedback to make a difference. Obviously, the person has to want to change. When a feedback recipient yawns at people trying to help and asks for an audiotape to play in the car instead of a multistep improvement plan, "we know not a lot will happen," says one counselor. Jeannie Rice, manager of buildings and property information at Vanderbilt University, spent a week at CCL. She says a few fellow attendees seemed determined not to change. "Their attitude was, 'I'm a butthead and I'm proud.'" To make the most of the process, experts say you should talk over the results with everyone who participated. At CCL, Rice learned that her thick Southern accent made her seem soft at first, but that colleagues called her "demanding, blunt, critical, and opinionated." When she returned to Vanderbilt, she sat down with staffers who had sent their anonymous comments to CCL. "A lot of them said, 'I didn't say that,'" she says with amusement. But it triggered a long discussion. "They said things like, 'Well, you used to be that way.'"

Ideally, your boss will have already had training from human-resources personnel on how to respond when you come for help. But with or without the boss, pick a small number of shortcomings to fix and decide on a few concrete remedies. A lousy listener? Find out which staffers are considered good at listening, and make it a point to watch them at work. Call a few staff meetings where your primary objective is to keep your mouth shut as much as possible. Ask a colleague to keep an eye on you and signal when you start slipping up. Exhausted just at the thought of all that self-improvement? Don't hold your breath waiting for feedback to go away. Its use is still expanding. Increasingly, chief executives are using the feedback process to promulgate their own special vision of the company to the troops. Says Peter Wentworth, director of management development at Warner-Lambert: "There's an old saying that you treasure what you measure." Therefore, when CEO Melvin Goodes articulated the corporation's values two years ago, "rather than press it into Lucite and stick it on the wall, we built a 360-feedback process around it." Now the drug company's employees grade one another on such traits as creativity, candor, and speed of action. A similar program exists at AT&T's business products division. Any manager supervising three or more people has to go through an evaluation every year pegged to the company's values statement and must share the results with + colleagues both up and down. Says Patricia Russo, head of AT&T's Global Business Communications Systems unit: "I think we're just beginning to see the power of this." So far, the feedback on feedback is positive.