Two decades of carefully-controlled randomized trials have established that sexual behavior change interventions can significantly reduce intervention participants' risk of acquiring HIV. There is abundant scientific evidence of the efficacy of these interventions when conducted in research settings with well-trained staff, sometimes substantial participant incentives, and the economic, human, and organizational resources that typify NIH-funded intervention research centers. However, the effectiveness of these interventions when implemented by frontline HIV prevention service providers is largely unknown. When implementing an evidence-based intervention, frontline service providers are apt to modify the original intervention in ways that best suit the organization's available resources, goals, and limitations. How these various factors influence the effectiveness of research-based interventions when implemented in the real world has received very limited attention. Based on the strength of evidence provided by randomized, controlled efficacy trials, the Centers for Disease Control and Prevention (CDC) has compiled a compendium of efficacious, evidence-based HIV prevention interventions. However, it is not known whether these interventions are effective when implemented in the real-world, by resource-constrained service providers; how these service providers adapt research- based interventions and how these modifications affect intervention effectiveness; how organizational, structural, and client-centered factors impact the ability of frontline service providers to effectively implement these interventions; or whether these interventions are cost-effective when implemented by frontline service providers. To address these critical research questions, the proposed study will evaluate the effectiveness and cost-effectiveness of DiClemente and Wingood's SISTA intervention for African American women, as implemented by 8 HIV prevention service providers that have completed the CDC's DEBI training for the SISTA intervention. The main analysis will assess the effectiveness and cost-effectiveness of the SISTA intervention as implemented by each of the service providers, and overall, across service providers. A mixed method (quantitative/qualitative) approach will be utilized to characterize intervention implementation, to study intervention adaptation processes, and to assess how service provider characteristics influence intervention fidelity and effectiveness. PUBLIC HEALTH RELEVANCE: The proposed study addresses a highly-significant question of great public health importance: Are evidence- based HIV prevention interventions effective when implemented by frontline service providers? NIH's substantial investment in the development of efficacious interventions comes to naught if these interventions cannot be effectively implemented by frontline HIV prevention service providers.