Objectives.The authors sought to identify associations between critical care nurses' self-reported participation in euthanasia, their social and professional characteristics, and their attitudes toward end-of-life care.Methods.Data were collected through an anonymous mail survey of 1,560 US critical care nurses, of whom 1,139 (73%) responded. Nurses were asked to report whether they had received requests to engage in euthanasia and whether they had engaged in euthanasia. In addition, nurses were asked to respond to items assessing their attitudes toward end-of-life care.Results.Of 852 nurses who identified themselves as practicing exclusively in adult intensive care units, 164 (19%) reported that they had engaged in euthanasia, 650 (76%) reported that they had not engaged in euthanasia, and 38 (4%) could not be classified. Only 30% of respondents believed that euthanasia is unethical. Logistic regression indicated that older nurses, more religious nurses, nurses practicing in cardiac care units, and nurses with less favorable attitudes toward euthanasia were significantly less likely to report having engaged in euthanasia, although the effects of age and religious beliefs appear to have been mediated by attitudes.Conclusions.These results help explain why some US critical care nurses engaged in euthanasia despite legal and professional prohibitions against it. Because critical care nurses may have a special understanding of the needs of critically ill patients, these results may indicate that current guidelines for end-of-life care are inadequate.