Research on behavioral HIV risk reduction interventions for injection drug users (IDUs) has focused on primary outcomes (e.g., reduced injection drug use, increased condom use) but has not fully examined the respective roles played by intervention components on these primary outcomes. In this paper, we present a structural equation modeling (SEM) approach in which we specify the causal pathways leading from theory-based intervention components to risk reduction outcomes among a sample of primarily IDUs (n = 226) participating in an inner-city community-based methadone maintenance program. Similar pathways were found leading to both drug- and sexual-related risk reduction outcomes. Findings suggest the importance of targeting participants' risk reduction motivation and behavioral skills versus employing more passive informational strategies. Findings also indicate that our intervention may be optimized by focusing more on participants' risk reduction motivation within the sexual-related content and placing equivalent emphasis on participants' risk reduction knowledge, motivation, and behavioral skills within the drug-related content. By quantifying the specific linkage between intervention components and risk reduction outcomes, our SEM findings offer empirical guidance for optimizing this intervention. This strategy may also serve as a useful theory- and data-driven means to inform the refinement of other behavioral interventions.