OBJECTIVE: To determine the clinical and demographic variables related to adherence to highly active antiretroviral therapy (HAART) in patients treated in our hospital and identify the characteristics of nonadherent patients. METHODS: Outpatients receiving treatment with HAART (n = 283) were asked about variables related to adherence and to complete the APGAR (family support), State-Trait Anxiety questionnaire (STAI) (emotional situation), and IAS (social support) questionnaires. Patients were classified in 2 groups depending on whether adherence was ≥95% or <95%. Adherence was defined as the percentage of dosage forms prescribed that were obtained by the patient at the hospital pharmacy. A multivariate analysis was created to analyze how each significant variable affected adherence. RESULTS: Our data showed significant nonadherence for patients with the following factors: low level of education, unemployed, emotional situation, and abuse of substances including intravenous drugs. All significant variables were included in a logistic regression model to optimize the results. This model considered 4 variables: age (95% CI 0.89 to 0.99), number of antiretroviral drugs (95% CI 1.05 to 2.11), STAI Anxiety/Trait test (95% CI 2.02 to 6.02), and abuse of drugs (95% CI 1.20 to 3.95). CONCLUSIONS: We recommended special intervention to reinforce adherence for younger patients, patients taking a high number of antiretroviral drugs, those who have a history of intravenous drug use, and those with high anxiety status.