Two hundred one patients of ventricular septal defect, which were operated at Seoul National University Hospital, were analysed on clinical background during the period from January, 1975 to December, 1980. The results were as follows: 1. Of the 201 patients, 118 patients were male [58.7%] and 83 patients were female [41.3%]. Their age ranged from 15 months to 40 years, and the mean age was 8.7 years. 40% of the patients were between 4 and 8 years. 2. The most common symptoms showed frequent U RI and exertional dyspnea. 3. On Kirklin`s anatomical classification, type I constituted 26.9%, type II 58.2%, type III 12.4%, and type IV 1.0%. We showed marked increased incidence of type I VSD as compared to Caucasians* 4. 46 cases were associated with other congenital cardiac diseases. They were PDA [13 cases], AI[11 ], ASD[6], PS[10], MI[4], and Double aortic arch [1]. 5. In 128 patients, who had complete hemodynamic data and were not associated with other congenital cardiac diseases, an attempt was made to correlate the EKG findings with the hemodynamic data, and defect size with the hemodynamic data. The children had variable distribution of PA syst. pr. and Rp/Rs. But most of adults had Rp/Rs of 0.15 or less. As Pp/Ps increased, the rate of operative complication increased also. 6. When a normal EKG pattern was present, Qp/Qs and Rp/Rs and Pp/Ps were relatively low. When EKG findings were LVH pattern, there was diastolic volume overload to left ventricle. As RVH, there was systolic pressure overload to right ventricle. And as BVH, there was mixed pattern of diastolic volume overload to left ventricle and systolic pressure overload to right ventricle. 7. Among patients in defect was less than 1 cm2 per M2 of BSA, Qp/Qs was less than 2:1, and Rp/Rs less than 0.25, and PAsyst. pr. less than 50 mmHg, and Pp/Ps was less than 0.5. But patients with the defect greater than 1 cm2 per M2 of BSA had no correlationship between Qp/Qs, Rp/Rs, PAsyst. pr. and defect size in each other. Most of patients with the defect greater than 2 cm2/M 2 BSA, Pp/Ps was greater than 0.5. 8. Operative mortality rate was 9.5% [19 cases] among 201 patients. And complication rate including mortality rate was 22.9% [46 cases]. [KTCS 1982;1:90-97]