Throughout this century there have been many efforts to reform the medical curriculum. These efforts have largely been unsuccessful in producing fundamental changes in the training of medical students. The author challenges the traditional notion that changes to medical education are most appropriately made at the level of the curriculum, or the formal educational programs and instruction provided to students. Instead, he proposes that the medical school is best thought of as a 'learning environment' and that reform initiatives must be undertaken with an eye to what students learn instead of what they are taught. This alternative framework distinguishes among three interrelated components of medical training: the formal curriculum, the informal curriculum, and the hidden curriculum. The author gives basic definitions of these concepts, and proposes that the hidden curriculum needs particular exploration. To uncover their institution's hidden curricula, he suggests that educators and administrators examine four areas: institutional policies, evaluation activities, resource-allocation decisions, and institutional 'slang'. He also describes how accreditation standards and processes might be reformed. He concludes with three recommendations for moving beyond curriculum reform to reconstruct the overall learning environment of medical education, including how best to move forward with the Medical School Objectives Project sponsored by the AAMC.