No national study of Hispanics has examined variation in HIV/AIDS-related knowledge by ethnicity, place of birth, and duration in the United States (for the foreign born) at least in part because of data constraints. Data from the 1991 and 1992 National Health Interview AIDS Supplements were used to examine the influence of these factors, and other sociodemographic and HIV/AIDS-related variables, on a 25-item HIV/AIDS knowledge scale. Descriptive and multivariate analyses indicate that foreign-born Hispanics with shorter durations in the United States have significantly lower levels of HIV/AIDS knowledge, as do those of Mexican and Cuban ethnicity. Numerous other factors, most of which are known to be associated with HIV/AIDS knowledge in the general population, were found to be significantly associated with HIV/AIDS knowledge among Hispanics in multivariate analyses; these include age, education, gender, rural residence, residence in the West, knowing a person with HIV/AIDS, personal risk for HIV/AIDS, and having been tested for HIV outside of the blood donation system. Results suggest that HIV/AIDS information campaigns targeted to Hispanics may not be equally effective in reaching foreign-born and U.S.-born subgroups or persons of differing ethnicities. Future studies should examine sources of HIV/AIDS information and the mechanisms of knowledge acquisition and transmission within specific subgroups of the Hispanic population.