The USA currently has the highest incarceration rate in the world. Individuals at greatest risk for HIV also tend to be among those at an elevated risk for incarceration. The HIV epidemic is driven by injection drug use and sexual behaviour, and estimates of prison-based sexual behaviour vary widely. This study examined sexual behaviour among 1,369 incarcerated men and women in the New York City area. Approximately 13 percent of the sample (n=176) reported being sexually active while incarcerated over the previous 6 months. Multiple logistic regression models were used to examine the predictors of prison sexual behaviour. The following variables were associated with increased odds of sexual activity within the previous six months: female gender (OR= 3.28; 95%CI=1.95,5.51), Black race (OR= 2.26; 95%CI=1.47,3.46), history of drug use (OR=1.85; 95% CI=1.04,3.30), bisexual (OR= 3.19; 95%CI=1.90,5.38) or homosexual identity (OR=8.50; 95% CI=3.92,18.43), and conjugal visitation programme participation (OR=66.26; 95%CI=31.42,139.74). Educational programmes regarding sexually transmitted infections and appropriate harm reduction measures are warranted for this population. The expansion of conjugal visitation programmes may also be useful in helping prisoners sustain their relationships with partners from their community and reduce the risk of infectious disease transmission in this environment.