This randomized clinical trial examined the relative efficacy of a relationship-based HIV/STI prevention intervention for women and their regular male sexual partners at 12 months post-intervention. A total of 217 couples were randomized to (1) a six-session intervention provided to the woman and her sexual partner together (n=81); (2) the same intervention provided to the woman alone (n=73); or (3) a one-session health information education "control" provided to the woman alone (n=63). Findings suggest the intervention was efficacious in reducing unprotected sex at 12 months post-intervention, compared with the education control group. No significant differences were observed when comparing whether couples received the intervention together or when the woman received it alone.