Forty nine patients [M: 31, F: 18], age from 2 months to 17 years [mean= 4.9 years], underwent operations, from April 1986 to December 1992, for the relief of subvalvular aortic stenosis in normal atrioventricular and ventriculoarterial connections.There were 4 anatomic types of subaortic stenosis : membranous in 29 cases [59.2%], fibromuscular in 11 [22.4%], diffuse tunnel type in 7 [14.3%], and miscellaneous in 2 cases. Thirty four patients [69.4%] had associated cardiac anomalies, of which ventricular septal defect was the most common [27 cases]. Other anomalies were patent ductus arteriosus, coarctation of the aorta, valvular aortic stenosis, double chambered right ventricle [DCRV], infundibular pulmonic stenosis, persistent left superior vena cava, and rigt aortic arch. Mean systolic pressure gradient between the left ventricle and ascending aorta was 26.4$pm$17.6 mmHg : 13.1$pm$17.6mmHg in the membranous type, 22.0$pm$18.4mmHg in the fibromucular type, and 56.1$pm$38.4mmHg in the diffuse tunnel type. Operative procedures were determined according to the type of subvalvular aortic stenosis : simple excision of subaortic membrane in the membranous type [29 cases], left ventricular myectomy with or without myotomy or fibrous tissue excision in the fibromuscular type [11 cases]. Among the 7 of diffuse tunnel type cases, ventricular myectomy was performed in 2 and a modified Konno operation was performed in 5 . Postoperative follow up was made with periodic echocardiography. The Mean postoperative follow up period was 33.8 months. There were 2 hospital mortalities [4.1%] and 2 late deaths. Residual stenosis remained in 3 cases and recurrence developed in 2 cases during the follow up period. 5 years actuarial survival rate was 91.8$pm$3.9% and 5 year complication free rate was 72.3$pm$10.4%. Conclusions : 1. Subvalvular aortic stenosis should be relieved completely as soon as possible when diagnosed, regardless of left ventricular outflow tract pressure gradient. 2. Good results were obtained using only simple excision of subaortic membrane in the membranous type of subaortic stenosis. However, aortoventriculoplasty [modified Konno prodedure] was necessary for good results in the diffuse tunnel type. 3. Periodic postoperative echocardiography was helpful in detecting the progression of residual stenosis and development of new stenosis.