In developing curricula for undergraduate and graduate medical education, educators have become increasingly aware of an interweaving of the formal, informal, and hidden curricula and their influences on the outcomes of teaching and learning. But, to date, there is little in the literature about the hidden curriculum of medical practice, which takes place after graduation and certification. This article initiates that discussion with influences of the hidden curriculum on the actions physicians take or do not take in caring for patients. Hafferty's framework of institutional policies, evaluation activities, resource-allocation decisions, and institutional slang, along with our knowledge of health services research and the continuing medical education (CME) research literature, suggests that there is a hidden and powerful curriculum that affects physician performance. Determining whether the hidden curriculum conflicts with the messages that we are delivering through formal CME (courses, clinical practice guidelines, peer review journals) may contribute to improving our impact on physician performance.