Using a pre- and post-test design with no control group, we evaluated the impact of a peer group intervention on work-related knowledge and behavior for health workers at an urban hospital in Malawi. We surveyed unmatched random samples of health workers, observed workers on the job, and interviewed clients about hospital services at baseline and at 6 months after the intervention. Universal precautions (UP) knowledge, reported hand washing, and reported client teaching were significantly higher at the final evaluation. The outcome differences remained robust in multivariate analyses with controls for demographic factors of age, gender, education, food security, and job category. Observations found consistently greater use of UP, more respectful interactions, and more client teaching at final evaluation. Patient surveys reported more discussion with health workers about HIV at the final evaluation. Peer-group interventions can prepare health workers in Malawi for HIV prevention and offer a potential model for other African countries.