This article presents data from an AIDS clinical trial that evaluated 238 (60 percent nonwhite) patients infected with HIV and their clinician's perceptions of medication adherence and visit attendance in relationship to lifestyle, psychosocial, and health belief model (HBM) variables. Twelve sites collected data via a prospective, multisite observational study design involving a companion study to a larger randomized clinical trial. Baseline information was collected by questionnaire and patient self-report on lifestyle; work and health-care experiences; available support; and psychosocial issues, including the HBM constructs. At follow-up visits, clinicians and patients graded medication adherence using the same scale. Patients confidentially reported follow-up information about lifestyle and answered HBM questions. After 12 months, adherence with study visits was associated with older age. Clinicians rated patients as having good adherence significantly more often when those patients were older, were employed at the time of enrollment, exhibited altruism as part of the reason for enrolling in the clinical trial, and thought HIV was very serious. Patients rated themselves as having good adherence significantly more often if they were older, had family or friends who were infected with HIV, and believed that being in the study was worth the trouble.