BACKGROUND Identifying sexually transmitted infections (STI) in HIV-infected individuals has potential to benefit individual and public health. There are few guidelines regarding routine STI screening in sub-Saharan African HIV programs. We determined sexual risk behavior and prevalence and correlates of STI in a national survey of large HIV treatment programs in Kenya. METHODS A mobile screening team visited 39 (95%) of the 42 largest HIV care programs in Kenya and enrolled participants using population-proportionate systematic sampling. Participants provided behavioral and clinical data. Genital and blood specimens were tested for trichomoniasis, gonorrhea, chlamydia, syphilis, and CD4 T-lymphocyte counts. RESULTS Among 1661 adults, 41% reported no sexual partners in the past 3 months. Among those who reported sex in the past 3 months, 63% of women reported condom use during this encounter compared with 77% of men (P < 0.001). Trichomoniasis was the most common STI in women (10.9%) and men (2.8%); prevalences of gonorrhea, chlamydia, and syphilis were low (<1%-2%). Among women, younger age (adjusted odds ratio [OR], 0.96 per year; 95% confidence interval [CI], 0.94-0.98) and primary school education or lower level (adjusted OR, 2.16; 95% CI, 1.37-3.40) were independently associated with trichomoniasis, whereas CD4 count, cotrimoxazole use, and reported condom use were not. Reported condom use at last sex was associated with reporting that the clinic provided condoms among both women (OR, 1.7; 95% CI, 1.17-2.35) and men (OR, 2.4; 95% CI, 1.18-4.82). CONCLUSIONS Women attending Kenyan HIV care programs had a 10.9% prevalence of trichomoniasis, suggesting that screening for this infection may be useful. Condom provision at clinics may enhance secondary HIV prevention efforts.