The approximately 1.2 million inmates in U.S. correctional institutions have a high prevalence of communicable diseases, such as human immunodeficiency virus (HIV) infection, tuberculosis, hepatitis B virus infection, and gonorrhea. Before their incarceration, most inmates had limited access to health care, which, together with poor compliance because of lifestyle, made them difficult to identify and treat in the general community. Because of the high yearly turnover (approximately 800% and 50% in jails and prisons, respectively), the criminal justice system can play an important public health role both during incarceration and in the immediate postrelease period. A public policy agenda for criminal justice should include an epidemiologic orientation, as well as resources for education, counseling, early detection, and treatment. Taking advantage of the period of confinement would serve both the individual and society by controlling communicable diseases in large urban communities.