The third edition of the American Psychiatric Association's Diagnostic and Statistical Manual (DSM-III; 1974) not only revolutionized psychiatric diagnosis, it transformed and dominated American psychiatry. The nosology of psychiatry had been conceptually confusing, difficult to apply, and bound to widely questioned theories. Psychiatry and clinical psychology had been struggling with their scientific status. DSM attempted to solve psychiatry's problems by making psychiatry more like its authors' perception of general medicine. It tried to avoid theory, especially psychoanalytic theories, by discussing only observable manifestations of disorders. But DSM is actually highly theory-bound. It implicitly and powerfully includes an exclusively "medical" model of psychological disturbance, while excluding other psychiatric ideas. Its authors tried to meet what they saw as "scientific standards." To a surprising extent, DSM reflects its creators' personal distaste for psychoanalysis. The result is that DSM rests on a narrow philosophical perspective. The consequences of its adoption are widespread: it has profoundly affected drug development and other therapeutic studies, psychiatric education, attitudes toward patients, the public perception of psychiatry, and administrative and legal decisions. This article explores how DSM's most problematic features arise from its history in psychiatric controversies of the 1960s and its underlying positivistic philosophy.