Not long ago organ transplants were headline news about frontier medicine; now they are commonplace. Today both the number of transplants and long-term survival are increasing. In addition, physicians have learned how to keep increasingly sick patients alive longer and how to make more people eligible for transplants. The dark cloud in this sunny picture is the shortage of donated organs. According to the United Network for Organ Sharing (UNOS), which coordinates transplant registration, 3448 people died in 1995 because organs were not available for them in time. Last summer there were about 47,000 Americans awaiting transplants, but if this year is similar to 1995, only about 40% of them will actually receive an organ. A third to a half of all people on waiting lists die before an organ can be found for them. This shortage raises several difficult ethical problems, which can only be outlined in the space available here. Topics discussed include: i) how should the limited supply of organs be distributed? ii) should donors be encouraged to donate by the use of financial incentives? iii) the definition of death; iv) animal donors; v) organs from healthy donors; and vi) the changing physician-patient relationship.