Abstract: Objective To investigate the clinical anatomy of ventricular septal defect(VSD) in tetralogy of Fallot(TOF)，reassess its classification and technique of surgical closure. Methods The data of one hundred consecutive patients with TOF (between January 2002 and June 2006) were reviewed. Their ages ranged from 2 months to 13 years, weights ranged from 5 to 38kg, percutaneous oxygen saturation(SpO2) ranged from 57％ to 92％, haematocrit(HCT) ranged from 0.34 to 0.74, Nakata index ranged from 90 to 210mm2/m2 and McGoon ratio ranged from 0.8 to 2.0. The clinic anatomy of the VSD was studied intraoperatively. Results Among them, seventy one patients had fibrous continuity between the leaflets of the aortic and tricuspid valve. Ninteen patients had a muscular postero-inferior border. Ten patients had subpulmonary VSD’s. There was no third degree atrioventricular block (3°AVB). Two patients had transient-atrioventricular dissociation but subsequent returned to sinus rhythm. Twenty two patients had incomplete right bundle branch block. Three patients were found to have very small residual VSD (less than 0.2cm) in the posteroinferior borders which closed spontaneously after 6 months. ConclusionVSD in TOF when classified as peri-membranous, muscular and subpulmonary VSD may improve the accuracy of surgical closure.