The clinical, radiological, electrocardiographic, and haemodynamic findings in 7 patients with the syndrome of congenital absence of the pulmonary valve with ventricular septal defect are reported. Findings included a pansystolic murmur and a low-pitched delayed diastolic murmur at the left sternal border with no pulmonary valve closure sound, an rsR' pattern in V1 on the electrocardiogram, and a chest x-ray showing a large heart and gross dilatation of the main, left or right pulmonary arteries but normal or reduced vascularity of the peripheral lung fields. Cardiac catheterization showed a left-to-right shunt at ventricular level in every case, though in one the shunt was bidirectional. Despite right ventricular systolic pressures at least 75 per cent of systemic level in every patient, the pulmonary artery pressure was invariably normal. Pulmonary stenosis was shown to exist at infundibular level, at valve ring level, or at both. Selective right ventricular angiography was diagnostic: the main and right or left pulmonary arteries were aneurysmally dilated and there was an abrupt transition in calibre between these vessels and their immediate branches; enlargement of the right pulmonary artery caused distortion and downward displacement of the left atrium in 4 patients; in 2 there was a flat ;diaphragm' in the pulmonary valve position.The diagnosis was confirmed in 3 patients by necropsy. The pulmonary valve was represented by at most a rudimentary fringe of tissue. Histological examination of the pulmonary arteries in one patient showed a correlation between the dilatation of the artery and the structure of its wall.