The character of idiopathic hypertrophic subaortic stenosis (IHSS) was studied retrospectively in a large community hospital for the six-year period, 1968--1974. Cases were discovered by examining the records of the Cardiac Non-Invasive Laboratory (phono- and echocardiography). Of the 46 cases of IHSS identified, 39 were in patients of the 50--81 age group. Thirty-two (82 percent) of the 39 patients were women, and 25 (78 percent) of these had a significant degree of hypertension. The hypertension had been present for more than five years in 62 percent of the cases. In 84 percent of the elderly females, the cardiac murmur had been present for less than ten years, and in 65 percent for less than five years. There was no family history of IHSS. Eighteen of the 46 IHSS patients underwent cardiac catheterization which confirmed the accuracy of the cardiographic data in all cases. The results of this study indicated that IHSS is usually nonfamilial, predominates in elderly females, and tends to be acquired after a lengthy period of hypertension. Cardiographic data appear highly specific diagnostically, often rendering cardiac catheterization unnecessary. Previous studies have not clearly defined the role of hypertension in the development of IHSS, at least partly because of the highly selective nature of most series reported from referral centers. These series often contain large numbers of younger patients.