A convenience sample of 587 subjects from the community health centers of Harris County, Texas, completed a structured interview that included questions on knowledge of AIDS transmission and prevention and on the Wallston Health Locus of Control (HLOC) Scale. HLOC score was a strong independent predictor of AIDS knowledge, with high externality associated with less knowledge. In a regression equation predicting AIDS knowledge, HLOC contributed 3% of the variance after education and ethnicity were accounted for. Hispanic and black individuals had a higher external orientation than white individuals. These findings suggest the need to address personal beliefs and perceptions concerning risk and to consider HLOC when educating patients and the public about AIDS.