Catheter closure of the patent ductus arteriosus is now a reality. The purpose of this study was to establish the prevalence of associated cardiovascular defects and the accuracy of echocardiography in patients referred for transvenous ductal closure. This study reviewed 146 patients seen from 1981 to 1988: 126 with only a patent ductus arteriosus (Group I) and 20 with additional cardiovascular anomalies (Group II). Groups I and II did not differ significantly in age, gender or physical examination except for the presence of a continuous murmur (Group I 100% versus Group II 80%, p less than 0.001). A left patent ductus arteriosus was visualized by two-dimensional echocardiography in 96% of patients and was evident by Doppler study in 100%. A patent ductus arteriosus was not seen in six patients including a patient who was found to have only a collateral network from the aorta to the main pulmonary artery. The 12 patients with noncardiovascular abnormalities such as Down's syndrome were more likely than the overall group to have additional cardiovascular anomalies (6 of 12, p = 0.001). The cardiovascular anomalies encountered were varied. Eight of the 20 patients with such anomalies had only a restrictive ventricular septal defect in addition to the patent ductus arteriosus. Significant anomalies found at catheterization included two thoracic arteriovenous malformations and an isolated right carotid artery draining into the right pulmonary artery by way of a right ductus arteriosus. This study indicates that echocardiography is an effective diagnostic technique in this patient group. A thorough cardiac catheterization with angiography should be performed before implantation of a ductal device.