Objective:A previous study empirically compared the effects of two HIV-prevention interventions for men who have sex with men: (i) a safer sex lecture, and (ii) the same lecture coupled with a 1.5 h skills-training group session. The skills-training intervention led to a significant increase in condom use at 12-month follow-up, compared with the lecture-only condition. The current study retrospectively assesses the incremental cost-effectiveness of skills training to determine whether it is worth the extra cost to add this component to an HIV-prevention intervention that would otherwise consist of a safer sex lecture only.Design:Standard techniques of incremental cost-utility analysis were employed.Methods:A societal perspective and a 5% discount rate were used. Cost categories assessed included: staff salary, fringe benefits, quality assurance, session materials, client transportation, client time valuation, and costs shared with other programs. A Bernoulli-process model of HIV transmission was used to estimate the number of HIV infections averted by the skills-training intervention component. For each infection averted, the discounted medical costs and quality-adjusted life years (QALY) saved were estimated. One- and multi-way sensitivity analyses were performed to assess the robustness of base-case results to changes in modeling assumptions.Results:Under base-case assumptions, the incremental cost of the skills training was less than $13,000 (or about $40 per person). The discounted medical costs averted by incrementally preventing HIV infections were over $170 000; more than 21 discounted QALY were saved. The cost per QALY saved was negative, indicating cost-savings. These results are robust to changes in most modeling assumptions. However, the model is moderately sensitive to changes in the per-contact risk of HIV transmission.Conclusions:Under most reasonable assumptions, the incremental costs of the skills training were outweighed by the medical costs saved. Thus, not only is skills training effective in reducing risky behavior, it is also cost-saving.