Few studies have examined the psychosocial factors associated with sexual transmission behaviors among HIV-positive men who have sex with men (MSM), heterosexual men (MSW) and women. We enrolled 1,050 sexually active HIV-positive patients at seven HIV clinics in six US cities as part of a clinic-based behavioral intervention. We describe the sexual transmission behaviors and examine demographic, clinical, psychosocial, and clinic prevention variables associated with unprotected anal or vaginal intercourse (UAVI). Twenty-three percent of MSM, 12.3% of MSW and 27.8% of women engaged in UAVI with partners perceived to be HIV-negative or of unknown serostatus. Among MSM and MSW, having multiple partners and lower self-efficacy were associated with increased odds of UAVI. Self-rating one's health status as excellent/very good was a risk factor for UAVI among MSM. Among women, binge drinking and stressful life events were associated with UAVI. These findings identify variables that warrant attention in targeted interventions.