THE AUTHORS EXAMINED THE PREVALENCE of clinically diagnosed hypertension among all American Indian and Alaska Native outpatients served in Indian Health Service (IHS) facilities in fiscal year 1992, and compared these rates with a similar analysis done in 1987. In this report they provided data on that analysis as well as on the association between hypertension and diabetes. The 1992 overall estimated age-adjusted prevalence of clinically diagnosed hypertension in adults older than age 15 was 10.4%, compared with 10.9% in 1987, a small but significant decrease. Considerable variation exists in hypertension prevalence rates in American Indian communities as analyzed by IHS service area. This report represents an attempt to use ambulatory patient care data to demonstrate a means for ongoing surveillance of a chronic disease for the entire service population of the IHS. This comprehensive data set represents approximately 60% of the entire U.S. American Indian and Alaska Native population. Based on the ongoing nature of this ambulatory patient care data system, this model for hypertension surveillance permits a unique opportunity for longitudinal evaluation of quality improvement efforts for the American Indian and Alaska Native populations served by the IHS.