Relationship power has been highlighted as a major factor influencing women's safer sex practices. Little research, however, has specifically examined relationship power in drug-involved women, a population with increased risk for HIV transmission. Using baseline data from a National Institute on Drug Abuse Clinical Trials Network multisite trial of a women's HIV prevention intervention in community-based drug treatment programs, this paper examined the association between sexual relationship power and unprotected vaginal or anal sex. The Sexual Relationship Power Scale, a measure of relationship control and decision-making dominance, was used to assess the association between power and unprotected sex in relationships with primary male partners. It was hypothesized that increased relationship power would be associated with decreased unprotected sexual occasions, after controlling for relevant empirical and theoretical covariates. Findings show a more complex picture of the association between power and sexual risk in this population, with a main effect in the hypothesized direction for decision-making dominance but not for relationship control. Possible explanations for these findings are discussed, and future research directions for examining power constructs and developing interventions targeting relationship power among drug-involved women are suggested.