BACKGROUND: The AIDS Drug Assistance Program (ADAP) provides antiretroviral medications to low-income individuals with HIV infection. METHODS: A prospective cohort study of ADAP utilization, measured using medication possession ratio (MPR), was conducted during the 2008 calendar year at the University of Alabama at Birmingham 1917 HIV Clinic. Multivariable ordinal logistic regression evaluated factors associated with ADAP utilization. RESULTS: Among 245 patients, MPR quartiles (Q) were the following: Q1<69 percent, Q2=69-83 percent, Q3=84-93 percent, Q4>93 percent. In ordinal logistic regression, younger age (OR=0.59 per 10 years; 95 percent CI=0.44-0.79), nonwhite males (2.18; 1.18-4.04), lower CD4 count (2.79 for <200 cells/mm(3) ; 1.44-5.43), and a history of alcohol abuse (2.11; 1.02-4.37) were associated with poor ADAP utilization. CONCLUSIONS: One quarter of ADAP enrollees had MPR below 69 percent, a level well below that associated with optimal HIV treatment outcomes, indicating a need for programmatic interventions to improve ADAP utilization.