A brief report in the 10 August 2000 issue of the New England Journal of Medicine described a case of conjoined twins and their separation at Childrens Hospital in Boston, Massachusetts. That report described the extraordinary surgery; immediately after birth, made possible by the use of computer-aided presurgical planning.[1] The media picked up the story, and a first page article appeared in The New York Times on the same day.[2] Two days earlier, on 8 August, conjoined twins were born in Malta in a case that stirred even media attention. Eventually they underwent surgical separation in the United Kingdom against the parents' wishes.[3] Reflecting on the case presented in the New England Journal of Medicine has led one of the coauthors of that report to enlist a bioethicist to help consider its ethical aspects. This essay is the outcome of that joint endeavor. The two cases are similar in important ways. Although the U.K. twins were conjoined at their pelves while the Massachussetts twins were conjoined at their chests and abdomens, in both cases, one of the twins was perfused with blood pumped by her twin sister's heart. This phenomenon is known as twin reversed arterial perfusion, and had not previously been reported in the medical literature in conjunction with conjoined twinning. Also, in both cases, both twins would ultimately have died had they not been separated. Finally, the expected outcome of both cases was comparable and is so far confirmed by the facts: one twin was sacrificed in the surgery, and the surviving twin will have a relatively normal development and lead a healthy life, although she may not be entirely free from complications. Both surgeries are without question remarkable accomplishments, and the use of computer-aided surgical planning in the Massachusetts case was a great technical advance. Yet while the individual cases seem to have turned out successfully from a medical perspective, they also have troubling social implications. want other parents with this problem to try to save their kids, said the father of the twins described in the New England Journal of Medicine.[2] He will probably have his wish. In the Massachusetts case, the parents accepted the need to bring about the death of one twin in order to save the other. We agree that, if the choice is between saving one twin or allowing both of them to die, it is, other things being equal, better to save one. But it is never the case that everything else is equal. Other factors are always involved. Perhaps most importantly, there are always other cases--other patients, other children, other social needs. What is striking about these cases are their implications for the allocation of scarce public health care resources. The New York Times reported that the treatment of the Massachusetts case cost more than $500,000, partly paid by the Medicaid programs in Massachussetts and New Jersey, and the rest absorbed by the hospitals. We believe that the cost may actually have been much more, given that it involved three surgical procedures and six months of hospital care, most of it in the intensive care unit. Assume, nonetheless, that the cost of the procedure was approximately $500,000. Much has been written both about escalating health care costs and the need for their containment, and about the questionable practices that health maintenance organizations and third party payers employ to limit costs. Yet there is now a widespread consensus that something must be done to limit health care costs. In a recent U.S. Supreme Court case involving a suit by a patient who was denied necessary tests, Justice David H. Souter bluntly declared that rationing health care was a legitimate public goal.[5] The case of the Massachusetts twins illustrates the difficulties that stand in the way of solving this problem, given how health care decisions are currently made. It is not difficult to estimate the significance of $500,000 for health care. …