(FORTUNE Magazine) – Last year, graphic designer Sheri Wood found out that she had thyroid cancer. Isolated from big-city medical resources--she lives in rural Versailles, Kentucky--she turned to the Web to learn more about her illness. Today, post-treatment and healthy, she's still logging on as a frequent visitor to Mediconsult.com's Cancer Emotional Support Group (www. mediconsult.com), which is monitored by a doctor and lets her share her experiences with other far-flung patients. "The Internet has been really wonderful for this," she says. "I got addicted."

The Internet has long been a rich source of medical information--information you're likely to ignore until you or a loved one gets sick. When that time comes, you'll find the Web can be a great place to go for help. Online bulletin boards are a natural medium for patient-support groups, especially for people in hard-to-reach places, like Sheri Wood. What's more, the Internet is searchable. Why hike to the medical library to dig through cumbersome volumes of the New England Journal of Medicine when you can stay at home, type "heart disease," and get much of what you need in a flash?

Using the Web can also help you deal with health care workers. Your doctor might be too tight-lipped, protective, or busy to explain things as fully as you'd like. But armed with information from the Internet, you can ask intelligent questions and draw him out. The way he reacts can help you assess his competence as well.

Finding the site that suits you best may require a bit of rooting around. In fact, the biggest obstacle you're likely to face online is information overload. Commercial services like CompuServe, with their scores of active support groups, can focus your search. But most of the action these days is on the Web; indeed, everyone in health care from the government to your HMO seems to be there, offering support groups, medical research, and advice.

A good way to find precisely the help you need is to start with a visit to a search engine, which will generate a list of sites tailored to any topic. Old standbys like Yahoo (www.yahoo.com) serve well, or you can try medical-specific search sites, like HealthAtoZ (www.healthatoz.com) and Achoo (www.achoo.com).

If you have serious questions about a disease, national health organizations' Websites are highly dependable. The American Medical Association (www.ama-assn.org) lists local physicians, while the Centers for Disease Control (www.cdc.gov) and the National Cancer Institute (wwwicic.nci. nih.gov) have excellent databases. Standout academic sites include Emory University's MedWeb (www.gen. emory.edu/MEDWEB), with amazing links for research, and the University of Pennsylvania's Oncolink (www.oncolink.upenn.edu), perhaps the Web authority on cancer.

One of the most approachable sites is the Mayo Clinic Health O@sis (www.mayo.ivi.com). It has easy-to-use sections on cardiac health and cancer, and lets you search for more esoteric topics. The information is hardly sugar-coated. One page deals with tongue maladies such as furred tongue and black hairy tongue, complete with blurbs and photos. This is pretty unsettling stuff, though the Health O@sis reassures the user that both disorders are treatable with a toothbrush. At the bottom of the page is a link that lets you ask, "Is it cancer?" (It's not.)

You can find pop medical advice too. A Web fave is Ask Dr. Weil (www.drweil.com), which features Q&A with Dr. Andrew Weil, the popular natural medicine specialist. A typical question might ask about alternative remedies for depression. Dr. Weil's suggestion: aerobic exercise or 300 mg of a 0.125% extract of Saint Johnswort three times a day. Even if you think that's so much hokum, you may want to visit Ask Dr. Weil for its links to other sites. The depression Q&A sends the user not only to the predictably New Age BuddhaNet Meditation Workshop but also to the Mental Health Net Depression Guide and to PharmInfoNet, both with comprehensive link lists.

Wherever you roam, beware. The Internet is an open forum for all kinds of quacks. If you use common sense, you should be okay: Information from the American Cancer Society's page will be more dependable than a note in a chat group. Some sites try to do the weeding for you. Mediconsult.com president Ian Sutcliffe says his editors have screened out dubious advice, including one participant's suggestion that cancer patients drink a bit of their own urine each morning. But you can't rely on gatekeepers. Never let cybermedicine replace your real-life physician.