The objective of this paper is to evaluate a peer education programme for female sex workers in Bali, Indonesia. Sex workers participated in face-to-face interviews and STD exams in August-September 1998. In October 1998 one woman from each of 30 clusters was selected to be a peer educator and received a 2-day training on AIDS, STDs, condom use, and condom negotiation. After training, the peer educators were visited twice a week by field workers to answer questions and offer support. All sex workers received group education every 2 months. In January-February 1999, the sex workers again participated in face-to-face interviews and examinations. One month after peer education training, only 50% of the peer educators were still working in the clusters where they were trained. To evaluate the impact of the peer educators, sex workers in clusters where a peer educator continued to work were compared with sex workers in clusters where women did not continue to work (n=189). In clusters where women continued to work, there were higher levels of AIDS knowledge (P < 0.05), STD knowledge (P < 0.05) and condom use (82 vs 73%, P=0.15). The prevalence of Neisseria gonorrhoeae infection was also lower in clusters with a peer educator (39% vs 55%, P=0.05) than in clusters without a peer educator.