The author traces the history of psychiatric nosology in the United States from its origins in the early nineteenth century to the introduction of DSM-I in 1952. Until World War I, psychiatrists were not interested in systematic classification, although they were concerned with diagnosis. The first official nosology, adopted in 1918, reflected the need to collect mental hospital data. The federal Bureau of the Census had a role in the development of this nosology in that it required such data. The publication of DSM-I marked an internal transformation that mirrored the growing dominance of psychodynamic and psychoanalytic psychiatry and the relative weakness of the biological tradition. This transformation occurred largely as a result of the lessons learned by psychiatrists during World War II. The author's basic argument is that nosology reflected not only psychiatric ideology but also other, external determinants at any given point in time.