This report describes the course and prognosis of four patients with Noonan syndrome and associated pulmonary lymphangiectasia. All patients had (1) superior deviation of the QRS axis in the frontal plane of the electrocardiogram; (2) moderate to severe valvular pulmonary stenosis, with an additional atrial septal defect secundum type present in two and a small ventricular septal defect in one; and (3) bilateral prominence of the pulmonary interstitial markings (dilated lymphatics), with or without accompanying pleural effusions on the chest radiographs. Surgical repair of the cardiac lesion may cause undue morbidity because of the interruption of the engorged pleural or mediastinal lymphatics.