Serum specimens that had been obtained for routine operational procedures from consecutive entering male inmates during Spring 1987 and the same calendar period in 1988 were tested to identify prevalence and risk groups for antibody to HTLV-I/II. Specimens were assayed for antibody to HTLV-I/II using ELISA, RIPA, and Western blot techniques. Demographics were compared by serostatus using chi 2 and Fisher's exact tests. Of the 1,932 inmates entering prison, 49.3% were 25 years of age or older, 70.1% were black, 62.4% were committed from the Baltimore metropolitan area, 34.1% were intravenous drug users, and 7.0% demonstrated antibody to HIV-1. Among 1,932 inmates, 18 (0.9%) were HTLV-I/II seropositive. All seropositives were black; age greater than 25 years old was significantly (p less than 0.01) associated with seropositivity. Reactivity to HTLV-I/II did not vary significantly by year of entry, HIV-1 serostatus, jurisdiction, offense category, or sentence. Prevalence of HTLV-I/II among incoming male inmates was elevated compared to available local population comparisons. Additional blinded epidemiological serosurveys of antibody to HTLV-I/II are indicated for prison populations in order to monitor the extent and scope of infection in this population.