['To evaluate the rate of discordance between patients and physicians on adherence to highly active antiretroviral therapy (HAART) and identify factors related to discordance in these two assessments.', 'Prospective, multicenter, cohort study (AdICONA) nested within the Italian Cohort Naive Antiretrovirals (ICONA) study.', 'Tertiary clinical centers.', 'The patients filled out a 16-item self-administered questionnaire on adherence to HAART. At the same time, physicians estimated the current HAART adherence of their patient.', 'Discordance between patient and physician on adherence to antiretroviral therapy.', 'From May 1999 to March 2000, 320 paired patient-physician assessments were obtained. Patients had a mean plasma HIV RNA of 315 copies/ml (64% had undetectable HIV RNA) and a mean CD4+ cell count of 577 cells x 10(6)/L. Nonadherence was reported by 30.9% of patients and estimated by physicians in 45.0% cases. In 111 cases (34.7%), patients and physicians were discordant on adherence to HAART. Kappa statistics was 0.27. Using patient-assessed adherence as reference, sensitivity, specificity, positive predictive value, and negative predictive value of physician-estimated adherence were 64.7%, 66.6%, 81.2%, and 45.8%, respectively. On multivariable analysis, low education level, unemployment, absence of a social worker in the clinical center, and unavailability of afternoon visits were significantly correlated with patient-physician discordance on adherence to antiretrovirals.'] Are patient-reported and physician-estimated adherence to HAART : social and clinic center-related factors associated with discordance?