BACKGROUND. Accurate information about acquired immunodeficiency syndrome (AIDS) and human immunodeficiency virus (HIV) is important for prevention. This study determined whether AIDS knowledge varied among populations residing in areas with a low, medium, or high incidence of AIDS. METHODS. Respondents to the 1988 National Health Interview Survey of AIDS Knowledge and Attitudes, which is based on a nationally representative sample of 29,659 adults, were rated on their knowledge about modes of HIV transmission, general knowledge about AIDS, and misperceptions about HIV transmission through casual contact. RESULTS. Persons 50 years of age or older, Blacks, Hispanics, and persons with less than a high school education had lower knowledge scores and higher misperception scores. Residents of the high-incidence area had more misperceptions than those who lived in the medium- or low-incidence areas. Sociodemographic determinants of scores were important factors overall and within each AIDS incidence area. CONCLUSIONS. These data suggest that the ability of educational messages to reach and be absorbed by individuals nationwide is less dependent on whether they live in an area with a high incidence of AIDS and more dependent on other demographic variables. New and continued efforts are needed to improve knowledge in older persons, minorities, and the less educated in all parts of the country.