This report describes the effects of a peer-group intervention on Malawian urban hospital workers' HIV-related personal knowledge, attitudes, and behaviors. More than 850 clinical and nonclinical hospital workers received the intervention. Evaluation used independent surveys of a sample of workers at baseline (N = 366) and postintervention (N = 561). Compared with the baseline survey, after the intervention, workers had higher knowledge of HIV transmission and prevention; more positive attitudes including more hope, less stigmatization of persons with HIV, more positive attitudes toward HIV testing and condom use, and higher self-efficacy for practicing safer sex and for community prevention; more reported recent personal HIV tests, more discussion of safer sex with partners, and more reported community HIV prevention activities. However, health workers' risky sexual behaviors did not differ at baseline and postintervention. The intervention should be strengthened to support more sexual risk reduction and be made available to all health workers in Malawi.