OBJECTIVES: We evaluated the prevalence of gonorrhea, chlamydia, trichomoniasis, and syphilis in patients entering residential drug treatment. METHODS: Data on sexual and substance abuse histories were collected. Participants provided specimens for chlamydia and gonorrhea ligase chain reaction testing. Trichomonas vaginalis culture, and syphilis serologic testing. RESULTS: Of 311 patients, crack cocaine use was reported by 67% and multisubstance use was reported by 71%. Sexually transmitted disease (STD) risk behaviors were common. The prevalence of infection was as follows: Chlamydia trachomatis, 2.3%; Neisseria gonorrhoeae, 1.6%; trichomoniasis, 43%; and syphilis, 6%. CONCLUSIONS: STD counseling and screening may be a useful adjunct to inpatient drug treatment.