Ethics and epistemology in medicine are more closely and more interestingly intertwined than is usually recognized. To explore this relationship, I present a case study, clinical trials of extracorporeal membrane oxygenation (ECMO; an intervention for persistent pulmonary hypertension of the newborn).Three separate ethical issues that arise from this case study—whether or not it is ethical to perform a certain trial at all, whether stopping rules for trials are ethically mandated, and the issue of informed consent—are all shown to be intimately related to epistemological judgments about the weight of evidence. Although ethical issues cannot, of course, be resolved by consideration of epistemological findings, I argue that no informed view of the ethical issues that are raised can be adopted without first taking an informed view of the evidential-epistemological ones.