Childhood sexual abuse (CSA) is associated with a wide range of negative outcomes. The authors investigated the relation between CSA and sexual risk behavior in 827 patients recruited from a sexually transmitted disease (STD) clinic. Overall, CSA was reported by 53% of women and 49% of men and was associated with greater sexual risk behavior, including more sexual partners, unprotected sex, and sex trading. Alcohol use for men and drug use for women mediated the relation between CSA and the number of sexual partners in the past 3 months; intimate partner violence mediated the relation between CSA and the number of episodes of unprotected sex in the past 3 months for women. These results document the prevalence of CSA among patients seeking care for an STD and can be used to tailor sexual risk reduction programs for individuals who were sexually abused.