Among 236 aortic valves surgically excised at the Mayo Clinic in 1990 (mean patient age, 66 years; age range, 10 to 92 years), 154 (65%) were stenotic, 58 (25%) were insufficient, and 24 (10%) were both stenotic and insufficient. Pure stenosis was related to calcification, and causes included degenerative (51%), bicuspid (36%), post-inflammatory (9%), and other (4%) reasons. Fourteen (9%) valves with pure stenosis also underwent ventricular septal myectomy, 12 for hypertrophy and two for co-existent hypertrophic cardiomyopathy. Pure insufficiency was not related to calcification, and causes included aortic root dilatation (50%), bicuspid valve (14%), post-inflammatory (14%), post-therapeutic (14%), and other (8%) reasons. Combined stenosis and insufficiency was secondary to degenerative calcification (46%), bicuspid and post-inflammatory etiologies (17% each), post-therapeutic (13%), and indeterminate (8%) causes. New observations include the following findings: (1) degenerative (senile) disease is the most common cause of aortic stenosis and combined stenosis and insufficiency at the Mayo Clinic, (2) aortic root dilatation is the most common cause of pure aortic insufficiency, (3) post-therapeutic aortic valve disease now leads to valve replacement in a substantial percentage of patients, particularly among those with insufficiency, (4) post-inflammatory (presumably rheumatic) disease is relatively uncommon in all three functional categories, (5) septal myectomy may be performed for hypertrophic states other than hypertrophic cardiomyopathy, and (6) adults with operated congenital heart disease are undergoing valve replacement for annular dilatation with insufficiency. Because of the increasing age of the general population, the prominence of age-related degenerative aortic valve calcification and aortic root dilatation may have important implications concerning future health care costs.