The current study utilized a sample of 123 inner-city drug users in residential treatment, comparing sexual risk behavior (SRB) across primary users of (a) heroin and not crack/cocaine, (b) crack/cocaine and not heroin, and (c) both heroin and crack/cocaine. Additional analyses also examined impulsivity as a mediator of drug choice and SRB. Results indicated that SRB was higher in primary crack/cocaine users than in primary heroin users, with those using both drugs evidencing intermediate levels of SRB. Beyond differences in SRB, a similar pattern across drugs was found for impulsivity. Finally, impulsivity mediated the relationship between drug choice and SRB. Although further research is necessary to establish causal relationships, these results support a relationship between SBR and crack/cocaine, and suggest that disinhibition processes including impulsivity may underlie this relationship.