Various interventions have been adopted to reduce HIV transmission among sex workers and their clients but the effectiveness of these strategies has yet to be investigated using meta-analytic techniques. To evaluate the effectiveness of behavioral interventions to reduce the transmission of HIV infection among sex workers and their clients in low- and middle-income countries. The Cochrane Central Register of Controlled Trials (CENTRAL), the Cochrane HIV/AIDS group specialized register, the Cochrane Database of Systematic Reviews, MEDLINE, PsycINFO, Sociological Abstracts, CINAHL, Dissertation Abstract International (DAI), EMBASE, LILACS, BIOSIS, SciSearch, INDMED, Proquest, and various South Asian abstracting databases were included in the database list. The publication sites of the World Health Organization, the US Centers for Disease Control and Prevention, and other international research and non-governmental organizations also appeared in the database list. Randomized controlled trials (RCTs) and quasi-RCTs examining the effects on HIV transmission risk of different behavioral interventions or comparing behavioral interventions with no intervention, where described any one of the outcome measures, such as HIV incidence and prevalence, STI incidence and prevalence, change in self-reported of condom use, and other HIV-related outcome. Two authors independently assessed trials, extracted data and assessed the risk bias. Heterogeneity amongst trials was also tested. A total of 13 trials with 8,698 participants were included. Primary outcomes (HIV and STI prevalence and incidence) were reported in seven trials. Of these, HIV incidence was reported in only three trials. After a 6-month follow-up assessment, there was no evidence that social cognitive behavioral intervention was effective in reducing HIV incidence (RR 0.12, 95% CI 0.01 to 2.22). However, there was a reduction in HIV incidence at 3-month follow-up assessment of promotion of female and male condom (RR 0.07, 95% CI 0.00 to 1.38). Social cognitive interventions and promotion of female and male condom use were significantly reduced STIs incidence (RR 0.57, 95% CI 0.34 to 0.96) and (RR 0.63, 95% CI 0.45 to 0.88), respectively. Secondary outcomes were identified in 13 trials. Meta-analyses showed evidence that interventions to promote the use of female and male condoms do reduce non-condom use (RR 0.83, 95% CI 0.65 to 1.05) compared to promotion of male condoms alone, and that social cognitive interventions reduced drug use among sex workers (RR 0.65, 95% CI 0.36 to 1.16) compared to standard care. Available evidence nevertheless suggests that compared with standard care or no intervention, behavioral interventions are effective in reducing HIV and the incidence of STIs amongst female sex workers (FSWs). Given the benefits of social cognitive theory and the promotion of condom use in reducing HIV/STI and the public health need to control transmission amongst FSWs, there is a clear finding in favour of behavioral interventions. However, it should be recognized that there is a lack of information about most other outcomes and target populations, and that all of the trials were conducted in low- and middle-income countries.