The aim of this cooperative study was to analyse the clinical profile of subvalvular aortic stenosis (SVAS) in adults. Thirty one cases were collected : patients aged 17 to 60 years (average 34 years). The diagnosis was confirmed in all patients either at surgery (30 cases) or at autopsy (1 case). The overall incidence of SVAS in patients with fixed obstruction to left ventricular ejection operated in the same period was 3.5%. Associated congenital malformations were detected in 15% of cases but intracardiac shunts were rare. Adult SVAS is a purer malformation than in children, probably because of spontaneous and surgical selection. The anatomical type of stenosing lesion in this series was a subaortic ring or membrane; 45% of patients, usually over 40 years of age (7 out of 9) had localised septal hypertrophy at the level of the diaphragmatic obstruction. The clinical presentation was that of mixed aortic disease with associated stenosis and regurgitation. Over 80% of patients had aortic incompetence diagnosed clinically (26 out of 31 cases) or on aortography (24 out of 25 cases); the regurgitant flow was assessed as mild in 15 cases, moderate in 6 cases and severe in 3 cases. There were obvious valvular lesions at surgery in 19 cases, especially in patients over 40 years of age (8 out of 9 cases). The mechanism was variable : non-specific (8 cases), destructive (6 cases), rheumatic (2 cases) or congenital (3 cases). Bacterial endocarditis was particularly common (26% of cases). Adult SVAS is a particularly difficult clinical diagnosis : the electrocardiogram and chest X-ray are not very informative.(ABSTRACT TRUNCATED AT 250 WORDS)