The effects of pulmonary vascular disease on the results of surgical closure of single large ventricular septal defects are reviewed. Hospital mortality in infants was not affected by the presence of preoperative pulmonary vascular disease. The late results were clearly related to age at operation, preoperative pulmonary vascular resistance, and pulmonary artery pressure. Probability of event analysis allows selection of the optimal age for elective repair of large ventricular septal defects.