Echocardiographic studies demonstrated the presence of coexisting idiopathic hypertrophic subaortic stenosis (IHSS) in 6 patients with aortic valve disease (4 calcific aortic stenosis, 2 pure aortic incompetence). The characteristics of IHSS were a narrow left ventricular outflow tract, a systolic anterior movement of the mitral valve (SAM), and asymmetric ventricular septal hypertrophy. Large SAMs were observed in 2 patients with pure aortic incompetence and one with aortic stenosis. Relatively small, inconstant, and often incomplete SAMs were noted in the remaining 3 patients with aortic stenosis. In contrast to isolated IHSS, the small SAMs observed in this group did not become prominent with the Valsalva maneuver or amyl nitrite inhalation. These features may be related to the afterload provided by the fixed, distal stenosis. Echocardiographic evidence of aortic valve disease was present in all patients. Clinically, coexistence of IHSS was not suspected in 5 patients. Associated IHSS was established using provocative measures during cardiac catheterization in 3 cases, while in the remainder it was substantiated at surgery. Three of 4 patients who underwent myotomy/myectomy concomitant with aortic valve replacement survived and postoperative echocardiographic studies revealed complete absence of SAMs in 2 of them. Echocardiography appears to be useful in the diagnosis of associated IHSS in the presence of aortic valve disease.