This study examined test-retest reliabilities of self-reported human immunodeficiency virus (HIV) sexual and drug injection behaviors among 246 prior drug users admitted to either of two residential drug treatment programs in Westborough, Massachusetts, and Providence, Rhode Island, between June 1990 and September 1992. Participants, selected by their date of admission, were administered admission and reliability questionnaires pertaining to HIV risk behaviors, the latter at approximately 2 weeks after admission. Estimated reliabilities (kappa coefficients) of the sexual behaviors ranged from 0.72 to 0.91; those for the drug injection variables ranged from 0.63 to 0.98. These results were consistent across groups defined by sex and injection of drugs. The consistently good reliabilities are significant to the design of independent studies of drug treatment populations utilizing self-report measures of sexual and drug behaviors.