We report a case complete atrioventricular defect with severe pulmonary hypertension. The patient was a girl aged 2 years and 6 months with Down's syndrome who had undergone pulmonary artery banding (PAB) 2 years previously. Postoperative catheterization after PAB showed severe pulmonary hypertension. Pulmonary resistance values were 9.3 and 7.3 units at 1 year and 5 months and 1 year and 9 months respectively. We performed re-PAB and lung biopsy when the patient was 2 years and 6 months old. The biopsy specimen at re-PAB classified as Heath-Edwards grade 3 and had an IPVD score of 1.7, indicating tolerance to radical operation. Six months after re-PAB, pulmonary vascular resistance decreased a level at which radical operation could be performed safely. Radical operation was performed 1 year and 4 months after re-PAB. The post operative course was uneventful, and pulmonary hypertensive crisis did not occur. The lung biopsy at the final operation was classified as Heath-Edwards grade 3, had an IPVD score of 1.1, and showed improvement when compared with the pathological findings at re-PAB.