The Health Belief Model (HBM) has been applied to a variety of health conditions: most are less threatening and require less complex responses than those arising in the case of AIDS. The utility of the HBM in understanding preventive behaviors in AIDS is examined in a cohort of homosexual men at two different time points. Longitudinal analyses estimated the relationship of indices assessing susceptibility, severity, benefits, and barriers, as well as sociodemographic factors, to sexual behavior across the next 18 months. Analyses further defined these associations in specific subgroups of participants, such as those initially at lower or higher risk. In general, measures of severity and socioeconomic advantage had the most consistently beneficial effect on various measures of behavior. Little or no beneficial effect was observed for other components of the HBM, notably a measure of perceived susceptibility. These analyses suggest that the special features of AIDS may require development of more adequate theoretical frameworks.