OBJECTIVE: To employ the behavioral model of health services use in examining the extent to which predisposing, enabling, and need factors explain the treatment of the HIV-positive population in the United States with highly active antiretroviral therapy (HAART). DATA SOURCE: A national probability sample of 2,776 adults under treatment for human immunodeficiency virus (HIV) infection. STUDY DESIGN: The article uses data from the baseline and six-month follow-up surveys. The key independent variables describe vulnerable population groups including women, drug users, ethnic minorities, and the less educated. The dependent variable is whether or not a respondent received HAART by December 1996. DATA COLLECTION: All interviews were conducted using computer-assisted personal interview instruments designed for this study. Ninety-two percent of the baseline interviews were conducted in person and the remainder over the telephone. PRINCIPAL FINDINGS: A multistage logit regression shows that the predisposing factors that have previously described vulnerable groups in the general population with limited access to medical care also define HIV-positive groups who are less likely to gain early access to HAART including women, injection drug users, African Americans, and the least educated (odds ratios, controlling for need, ranged from 0.35 to 0.59). CONCLUSIONS: Those HIV-positive persons with the greatest need (defined by a low CD4 count) are most likely to have early access to HAART, which suggests equitable access. However, some predisposing and enabling variables continue to be important as well, suggesting inequitable access, especially for African Americans and lower-income groups. Policymakers and clinicians need to be sensitized to the continued problems of African Americans and other vulnerable populations in gaining access to such potentially beneficial therapies. Higher income, anonymous test sites, and same-day appointments are important enabling resources.