As a result of changes in the epidemiology of the HIV epidemic and in criminal justice policies over the past 2 decades, HIV infection in the United States has become concentrated in prisons and jails. The widespread incarceration of persons with or at risk for HIV infection has important public health ramifications, including but not limited to the intraprison spread of the virus. Incarceration, particularly of large numbers of men, can be socially disruptive and , in communities where incarceration is prevalent, can facilitate the spread of HIV infection. Interventions to enhance identification of infected inmates, prevention counseling, and treatment of inmates with HIV/AIDS are required to stem the contribution of incarceration to the spread of HIV infection.