Pulmonary stenosis is the most frequent problem after arterial switch operation for TGA. We experienced four cases of late severe pulmonary stenosis out of twelve patients. All four had supravalvular stenosis either at anastomotic site or at previously banded segment. One patient had associated valvular stenosis and another had bilateral branch stenosis. It is possible that valvular stenosis was due to retraction of equine pericardial patch and branch stenosis was due to overdistension. All four cases were successfully reoperated on 13∼39 months after switch operation. To prevent late pulmonary stenosis, we now alter technique of switch operation in two points. First, the great arteries are anastomosed with interrupted U-shaped sutures from outside of the vessels in whole circumference. Second, both coronary arteries are transferred with punched-out method to save tissue of Valsalva sinus, and the defects are closed with autologous pericardial patch.