Childhood sexual abuse (CSA) is related to poorer health outcomes, associated with increased risk for HIV acquisition, and prevalent among HIV risk groups. Links between CSA and health behavior are an important health concern. We examined the relationship between CSA and transmission risk behavior and medication adherence in 119 HIV-infected individuals with an injection drug use history. 47% reported CSA, with no gender difference. Individuals who experienced CSA were more likely to report sexual HIV transmission risk behavior in the past 6 months, more sexual partners, use of heroin in the past 30 days, and worse adherence to HIV medication than those who did not. These findings confirm that rates of CSA are high in this population, and suggest that a history of CSA may place people managing both HIV and opioid dependence at increased risk for HIV transmission, poor adherence to medication, and vulnerability to substance use relapse.