We examine community collectivization among female sex workers (FSWs) and high-risk men who have sex with men and transgenders (HR-MSM) following several years of HIV prevention programming with these populations, and its association with selected outcome indicators measuring individual behaviors (condom use with different partners and sexually transmitted infection [STI] treatment-seeking from government health facilities). Data for this study were collected from a large-scale cross-sectional survey conducted in 2010-2011 among FSWs (sample size: 3557) and HR-MSM (sample size: 2399) in Andhra Pradesh, India. We measured collectivization among FSWs in terms of three binary (low, high) indices of collective efficacy, collective agency, and collective action. Collectivization among HR-MSM was measured by participation in a public event (no, yes), and a binary (low, high) index of collective efficacy. Adjusted odds ratios (adjusted OR) and their 95% confidence intervals (CI) were computed to assess the relationships between collectivization and outcome indicators directly and through mediation of variables such as self-efficacy for condom use and utilization of government health facilities. Results show that among FSWs, high levels of collective efficacy (adjusted OR: 1.3, 95% CI: 1.1-1.7) and collective action (adjusted OR:1.3, 95% CI: 1.1-1.8) were associated with consistent condom use (CCU) with regular clients. Among HR-MSM, participation in a public event (adjusted OR: 2.7, 95% CI: 2.0-3.6) and collective efficacy (adjusted OR: 1.9, 95% CI: 1.5-2.3) were correlated with condom use with paying partners. The association between collectivization and outcome indicators continued to be significant in most cases even after adjusting for the potential mediators. Indicators of collectivization exhibited significant positive association with self-efficacy for condom use and service utilization from government health facilities among both FSWs and HR-MSM. The association of high levels of collectivization with CCU, STI treatment-seeking from government health facilities, ability to negotiate for condom use, and self-efficacy in utilizing government health facilities is relevant to effort to improve the effectiveness and sustainability of HIV prevention programs in India and beyond.