A questionnaire administered to inmates in two maximum- security prisons in Reynosa and Matamoros, each holding about 1,500 inmates, elicited information on respondent knowledge and behavior relevant to AIDS. Of 125 questionnaires disseminated at each prison, 80 were returned at Reynosa and 57 were returned at Matamoros. The final sample consisted of 109 males and 22 females. Among male respondents, 83 percent said their sexual orientation was heterosexual; 4 percent were homosexual, and 12 percent were bisexual. Prisoners were well aware of the manner in which AIDS is transmitted and understood that AIDS is not transmitted through casual contact. With respect to high-risk behavior, most respondents realized that prostitutes may carry the AIDS virus, and 90 percent were charged with drug-related offenses. Only 6.8 percent, however, admitted to intravenous drug abuse. The prevalence of AIDS, intravenous drug use, sexual behavior, and AIDS policies are compared for Mexican and U.S. prisons. 32 references, 12 notes, and 1 table