We report on an adult patient with discrete-type subaortic stenosis. A 48-year-old man who had progressed asymptomatically since childhood despite heart murmur was transferred to our hospital. The patient was diagnosed as having severe aortic stenosis with a pressure gradient of 100 mmHg across the aortic valve, associated with a grade II aortic regurgitation. A conventional aortic valve replacement was scheduled. During surgery, the aortic valve was found to be tricuspid but incompetent as a result of shrinking and thickening of the left coronary cusp. A circumferential fibromuscular ridge was observed under the cusps, which corresponded to Kelly's type II discrete subaortic stenosis. Because of the small subaortic area and deformity of the cusp, we performed aortic valve replacement after excision of all cusps and the fibromuscular ridge. Early corrective surgery is recommended for discrete subaortic stenosis to prevention regurgitation progression.