The Sonagachi Project of Kolkata, India has been recognized as a model community development and human immunodeficiency virus/sexually transmitted infection (HIV/STI) prevention intervention among female sex workers. Limited research has been conducted regarding its applicability outside the South Asian context. This study sought to document the process and effectiveness of integrating community development activities based on the Sonagachi model into an ongoing HIV/STI peer education program with female sex workers in Rio de Janeiro, Brazil. Structured cross-sectional surveys examining HIV/STI-related behaviors and community development measures were conducted among approximately 500 sex workers at pre- and post-intervention. We found that several community development components including social cohesion and mutual aid were significantly associated with consistent condom use among sex workers and their paying clients at pre-intervention. However, only a minority of women actively engaged in community-building activities over the 18-month study period. In turn, limited changes in community development components and no significant increases in the HIV/STI-related protective behaviors assessed were documented. Findings indicate that internalized stigma and socioeconomic pressures may have constrained the scope and pace of community mobilization in this setting during the study observation period.