The effects of a community popular opinion leader (CPOL) intervention were examined among market vendors in a city on the eastern coast of China. Employees of 40 food markets were enrolled in a study that provided HIV-related education and tests, and treatment for sexually transmitted diseases (STDs). Twenty markets were randomly assigned to a CPOL intervention (N = 1,695) and 20 markets to a control condition (N = 1,616). Market employees in the intervention condition reported positive attitudes regarding STD/HIV prevention and more frequent discussions about safe sex than those in the control condition. Compared with baseline, the prevalence of unprotected sexual acts and new STDs were significantly lower within each study condition 24 months later. Although the CPOL intervention achieved its goal of shifting attitudes within food markets, the gains did not lead to the expected behavioral and biological outcomes.