Sex workers have high rates of sexually transmitted infections (STIs), many of them easily curable with antibiotics. STIs as co-factors and frequent unprotected exposure put sex workers at high risk of acquiring HIV and transmitting STIs and HIV to clients and other partners. Eliminating STIs reduces the efficiency of HIV transmission in the highest-risk commercial sex contacts--those where condoms are not used. This paper reviews two STI treatment strategies that have proven effective with female sex workers and their clients. 1) Clinical services with regular screening have reported increases in condom use and reductions in STI and HIV prevalence. Such services include a strong peer education and empowerment component, emphasize consistent condom use, provide effective treatment for both symptomatic and asymptomatic STIs, and begin to address larger social, economic and human rights issues that increase vulnerability and risk. 2) Presumptive treatment of sex workers, a form of epidemiologic treatment, can be an effective short-term measure to rapidly reduce STI rates. Once prevalence rates are brought down, however, other longer-term strategies are required. Effective preventive and curative STI services for sex workers are key to the control of sexually transmitted infections, including HIV, and are highly synergistic with other HIV prevention efforts.