Prevalence of antibody to the human immunodeficiency virus type 1 (HIV-1) was assessed among 10 994 consecutive male and female entrants to 10 correctional systems in the United States. The HIV-1 seroprevalence for the 10 systems ranged from 2.1% to 7.6% for men and 2.5% to 14.7% for women; seroprevalence among women was higher than among men across nine of 10 systems. Using age 25 years to divide the population, HIV-1 prevalence among young women (5.2%) was significantly higher than among young men (2.3%), but similar to that in both older women (5.3%) and older men (5.6%). Overall, HIV-1 rates for nonwhites (4.8%) were higher than those for whites (2.5%). Although categories were identified across correctional systems, which may serve to focus prevention programs, variability in rates among correctional systems indicates that program planning must take local conditions into consideration.