Twenty-five patients with discrete subaortic stenosis were reviewed. Twenty were operated on for severe obstruction. Review of available data suggests there is a wide spectrum of the disease which may be divided into two main types designated I and II. Type I is a thin discrete membrane immediately under the aortic valve obstructing the outflow but not associated with narrowing of it. Type II is situated about 1 cm below the valve and consists of a fibrous ring, thicker than type I, and associated with muscular hypertrophy which narrows the outflow tract, encroaches on the anterior leaflet of the mitral valve, and may extend 1-2 cm downward. Both have a characteristic angiographic appearance. Results of surgery are good for type I but not satisfactory for type II. Aortic incompetence is likely to increase or develop following operation in both types.