To date, relatively few programs have been evaluated that were designed to affect the clinical practice patterns of primary care physicians who treat patients with hypertension. In particular, studies that have evaluated blood pressure control as a clinical outcome before and after an intervention are lacking. The Hypertension Management Program, developed by Applied Health Outcomes, is a quality improvement program designed to improve the medical management of hypertension in population-based health care settings. This program is in the process of continuing to collect baseline data from health maintenance organizations, conducting physician-focused interventions designed for improving clinical care, and collecting postintervention data between 6 and 12 months after the intervention is completed to determine its effect. The authors present the rationale for conducting large-scale hypertension management programs that measure outcomes, as well as preliminary baseline and postintervention data from the Hypertension Management Program, based on a current database of more than 1.9 million individuals enrolled in eight health care plans.