Agenesis of the hemidiaphragm is unusual congenital anomaly associated with a high mortality. A case of congenital agenesis of left diaphragm was experienced in 22-day old male patient who was dyspneic and cyanotic on admission. Emergency exploration through the left eight interspace thoracotomy showed complete agenesis of the left diaphragm. The stomach and transverse colon covered with peritoneal sac was partially herniated into left hemithorax. The left lung was slightly hypoplastic. This neonate had no intestinal malrotation. The defect was reconstructed using Dacron graft. Dacron patch was sutured with interrupted Ethibond to chest wall anteriorly, esophagus aorta and costomediastinal sinus medially, and the tenth rib posterolaterally. Postoperatively, Extubation was performed at 1st day, but some respiratory difficulty was noted. Severe dyspnea was occurred at postoperative 11th day and so reintubation was done. Intermittently ventilatory support and intravenous alimentation were continued for 9 days after that. Thereafter he had no respiratory problems at discharge.