Spurred by a severe shortage of cadaveric organs, there has been a marked growth in living organ donation over the past several years. This has stimulated renewed interest in the ethics of this practice. The major concern has always been the possibility that a physician may seriously harm one person while trying to improve the well-being of another. As Carl Elliott points out, this puts the donor's physician in a difficult predicament: when evaluating a person who volunteers to donate an organ, “a doctor is in the position of deciding not simply whether a subject's choice is reasonable … but whether he [the doctor] is morally justified in helping the subject accomplish it.”1 This question has become even more difficult since the introduction of living donor operations that are more risky than living kidney donation (e.g., adult-to-adult liver donation) and the suggestion that volunteers at added risk may sometimes be acceptable.2 So, how can we decide when the risk is too much?