This quasi-experimental, proof-of-concept study evaluated the effects of an intervention designed to help Nigerian men decrease risk for HIV/sexually transmitted infections and unintended pregnancy. The intervention was delivered in groups during two 5-hour workshops, with a monthly 2-hour check-in session. A comparison condition consisted of a group-based half-day didactic workshop. Based on recruitment area, 149 men were assigned to the intervention and 132 to the comparison. Men were evaluated at baseline and 3-month post-intervention. At follow-up, men assigned to the intervention were almost four times more likely than comparison men to report condom use at last intercourse (P < 0.001) and to report fewer unprotected vaginal sex occasions, greater self-efficacy for negotiation, a more egalitarian power dynamic in their primary relationship, more positive expectations for condom use and greater intention for future consistent condom use (all P values < 0.05). Findings suggest that this intervention is both feasible and effective.