The Konno procedure provides adequate relief of diffuse subaortic stenosis but requires aortic valve replacement. This may be questionable in patients without aortic valve lesions. Eleven patients had diffuse subaortic stenosis and normal aortic orifice: tunnel subaortic stenosis (6 patients) or diffuse hypertrophic obstructive cardiomyopathy (5 patients). The mean age was 16 +/- 14 years (range: 3 months to 45 years). The mean subaortic gradient was 95 +/- 24 mmHg (range: 60 to 150 mmHg). Two patients had previously undergone resection of discrete subaortic stenosis. Modified Konno procedures were used: aortoseptal approach with aortic annulus division in 5 patients, conal enlargement without aortic annulus division in 6 patients. There was one early death (9%, 70% CL = 1%-27%) and no late deaths. Reoperation was required in two patients: one early for iatrogenic aortic regurgitation and one late for residual ventricular septal defect and mitral regurgitation. The mean follow-up was 3.8 +/- 4.2 years (range: 2 months to 10 years). The survivors were in functional class I (8/10), had a normal left ventricular function (9/10), were in sinus rhythm (10/10) and had left ventricular outflow tract gradients ranging up to 25 mmHg (mean = 6 +/- 10 mmHg). Residual surgery-related defects included ventricular septal defect (one) and aortic regurgitation (one). In patients with diffuse subaortic stenosis and normal aortic orifice, modified Konno procedures with aortic valve preservation are preferable, effective and can be safely performed in infants and children.