Aortic valve prolapse is found in over 5% of children with ventricular septal defect (VSD). Although this association occurs mostly with doubly committed subarterial VSDs, in this study the predominant type of VSD was perimembranous. In order to determine the need and timing for surgery and whether the anatomical features of septal defect may influence clinical management and outcome in this lesion, we reviewed our experience with 28 consecutive patients, operated on for VSD with prolapsed aortic valve cusp, with or without aortic regurgitation. Twenty-two patients had a perimembranous VSD and six had doubly committed VSD. Aortic regurgitation was trivial or absent in nine patients, mild in ten and moderate to severe in nine. Associated cardiac anomalies were present in 18 patients, all having perimembranous VSD, and included right ventricular outflow tract (RVOT) obstruction (n = 6), discrete subaortic membrane (n = 4) or both (n = 8). None of these patients had more than moderate aortic regurgitation. The patients underwent surgical closure of the septal defect between the ages of 1.5 and 34 years of age (median = 7). Sixteen patients having mild or trivial aortic regurgitation underwent closure of the VSD only, and 12 patients underwent VSD closure with aortic valvuloplasty. Valvuloplasty was required more often in doubly committed VSDs (66%) and in the perimembranous type without associated anomalies (100%), and significantly less often in the presence of RVOT obstruction, subaortic membrane or both (22%). At follow-up (up to 5 years, mean 18 months), the grade of aortic regurgitation was unchanged in 11 and decreased in 5 patients undergoing closure of the VSD only.(ABSTRACT TRUNCATED AT 250 WORDS)