Non-adherence to medical regimens is a critical threat to the health of HIV-infected individuals. Patients who do not adhere to routine medical care cannot fully benefit from the increasingly efficacious treatments available to them. Consistent attendance at medical appointments plays a central role in both prolonging life and enhancing quality of life for persons living with HIV/AIDS. By identifying why many patients do not reliably attend medical services, interventions can be undertaken to improve appointment-keeping. The primary purpose of the present study was to identify factors predictive of HIV-related medical appointment attendance. One-hundred-and-forty-four outpatients in a public hospital ambulatory care HIV clinic were followed for seven months. Demographic, medical care and psychosocial factors were measured in order to prospectively predict the percentage of missed clinic appointments by persons with HIV disease. Greater outpatient appointment non-attendance was associated with younger age, minority status, less severe illness and lower perceived social support. Treatment duration, provider consistency, hopelessness and religious coping did not emerge as significant predictors of outpatient appointment-keeping in this sample. Practical and theoretical implications of these findings are discussed in light of recent medical advances in HIV/AIDS care.