This article reports the results of a peer-led HIV prevention education and condom promotion program among transport workers in Kaolack, Senegal. As part of a 2-year longitudinal follow-up study, changes in men's AIDS-related knowledge, sexual behavior, condom use, and perceived barriers to condom use were evaluated by self-reports obtained from a systematic sample of transport workers interviewed before and after intervention. In addition to men's self-reports, preintervention and postintervention data on men's sexual and condom use behavior were gathered from a sample of licensed, commercial sex workers, who cited transport workers as their primary source of clients. Significant increases in men's HIV-related knowledge, previous use of condoms (from 30.4% to 53.5%), and consistent condom use with regular sex partners were documented over the study period, as were significant declines in perceived barriers to condom use. Though men reported significantly fewer sexual encounters with casual and commercial partners at follow-up compared to baseline, these data were unreliable. Women's postintervention reports indicate that a greater proportion of clients (including, but not limited to transport workers) "always" agree to use condoms (p < .01) compared with baseline and that fewer men offer more money for unprotected sex (p < .01). However, women also report taking greater initiative in the mechanics of condom use (supplying the condom, putting it on, and taking it off) than they did prior to the intervention, and significantly (p < .05) fewer women think that most of their clients know how to use a condom. The findings indicate that the peer-mediated intervention had a positive impact on several important outcomes measured and suggest that HIV prevention efforts need to focus on male client groups despite the logistical and methodological challenges.