How is it possible? What are the personal, professional and political contexts that allow physicians to use their skills to torture and kill rather than heal? What are the psychological characteristics and the social, cultural and political factors that predispose physicians to participate in human rights abuses? What can be done to recognize at-risk situations and attempt to provide corrective or preventive strategies? This article examines case studies from Nazi Germany in an attempt to answer these questions. Subjects discussed include the psychology of the individual perpetrator, dehumanization, numbing, splitting, omnipotence, medicalization, group dynamics, obedience to authority, diffusion of responsibility, theories of aggression, training, cultural and social contexts, accountability and prevention.