Parents have known since time immemorial, and social scientists have agreed since the turn of the last century, that adolescents are "a people unto themselves"-a distinct developmental category. Yet it was not until the 1950s that a medical subspecialty focusing specifically on teenagers came into being. This article examines the interplay between the emergence of adolescent medicine and changes in American family relationships, youth culture, popular perceptions about young people, and the social experience of adolescence. The author traces the development of adolescent medicine from its origins in the works of J. Roswell Gallagher at Boston Children's Hospital in the 1950s to its uncertain prospects today, when, despite heightened recognition of their specific medical needs, most adolescents still receive inadequate health care.