(FORTUNE Magazine) – If a patient is suffering from progressive primary biliary cirrhosis, a fatal liver disease, there are two possible scenarios: (1) He dies, which until not long ago was the only outcome; (2) He receives a liver transplant and has a long and happy life.

While the second option is obviously the preferred one, it's by no means a given. First, about 80,000 people are on the various waiting lists for organs, and more than 6,000 of those people die each year. Second, the body's immune system is programmed to fight foreign invaders. Fortunately, the emergence and refinement of immunosuppressive (anti-rejection) drugs have shifted the odds in the transplant patient's favor. The three-year survival rate for a kidney transplant is now above 90%, while the rate for heart or liver transplants is above 75%.

Organ transplant operations have been an option for only about 40 years. It's now possible to transplant kidneys, hearts, livers, corneas, bone marrow, stem cells, lungs, and even intestines. A pancreas can be transplanted into a diabetic patient, enabling the body to restart its insulin production.

Of the more than 23,000 transplants performed each year, some 25% involve organs from living donors. The rest come from deceased donors, who generally provide multiple organs. Those from a sibling or other close living relative (who would typically contribute one kidney or one lobe of a liver) provide the best immune-system match and tend to survive better than organs from deceased donors.

In recent years both transplant recipients and donors have been getting older. Pediatric patients (under 18) receive only about 7% of all transplants.

Complications and recovery time depend on what's being transplanted. The most common transplant is a kidney, which can now be removed from a living donor by laparoscopic surgery. This involves careful isolation of one of the kidneys through a few small holes in the abdomen, then removal through an extended incision. It's easier on the donor, with decreased hospital time and faster recovery.

Putting that kidney into someone else takes about three hours. The nonfunctioning kidneys are usually not removed; the new kidney is placed in the pelvis. Patients are often up the day after surgery and out of the hospital in three to five days. Barring complications, they may be back to work in three to six weeks. Heart and liver transplant patients need more time. Because the immunosuppressive drugs must be taken for life, transplant patients' immune systems don't function optimally, and they're susceptible to a host of unusual infections and even some cancers.

The amount of time a patient spends on the National Patient Waiting List depends on the type of organ, the type and severity of the illness, the length of time already spent waiting, the body size of the recipient, the number of donors in a region, and blood and tissue type. Younger people are generally given higher preference. Organs from living donors are a good alternative to waiting for a cadaver organ.

In most states it's necessary to obtain permission from the family to use an organ from someone who has died, even if the driver's license indicates the desire to be a donor. Although a few states have recently changed their rules, if a potential donor hasn't discussed the matter with the family ahead of time, in many cases the organs aren't donated.

If you'd like to be an organ donor, talk to your family. Add donor status to your driver's license or fill out the card available at www.organdonor.com. Another way to help is to enroll in the American Bone Marrow Donor Registry (800-745-2452). Small decisions made now can lead to miracles further down the road.

Donald D. Hensrud, MD, is director of the Mayo Clinic Executive Health Program. For more on this topic, go to mayoclinic.com. Mayo Clinic offers Executive Health Programs in Jacksonville, Fla.; Rochester, Minn.; and Scottsdale, Ariz.