Custodial experience was common (79 percent in custody at some time, recent (58 percent in custody since 1987), and sentences were short (for 64 percent the most recent period of custody lasted one month or less). Injecting during last period in custody was reported by 23 percent, and 75 percent of those who injected in custody reported that they had shared needles and syringes. Sexual activity in custody was reported by 6 percent of the custodial sample. HIV positivity was self-reported by 12 percent of the custodial sample. Of the custodial group, those who were HIV positive were more likely then the HIV negative group to report injecting the syringe-sharing in custody. Outside custody (in the community) many (46 percent) had shared syringes during the previous 4 weeks, 83 percent had sexual partners during the previous 3 months, and 50 percent of these had sexual partners who did not themselves inject drugs. The findings indicate the potential for HIV infection to occur within custodial settings. 21 references. 3 tables. (Author abstract)