This study employed multivariate analyses and structural modeling procedures to examine a model for the determinants of adherence to medical regimens. Fifty adult hypertensive patients at a health maintenance organization completed questionnaires and participated in home interviews over a 10-week period. Knowledge of medical regimens, information communication between the patient and the medical professionals, satisfaction with health-care providers, health locus of control, social support, and treatment disruption to life-style were assessed. Adherence was assessed through self-report and behavioral (i.e., pill-count ratio, percentage of kept medical appointments) indices. Finally, repeated blood-pressure measurements were obtained. Structural modeling procedures revealed that greater expectancy for internal control over health and hypertension, greater knowledge of the treatment regimen, and stronger social support were significant determinants of adherence; in turn, higher levels of adherence facilitated blood-pressure reduction.