This review presents the cardiac and non-cardiac malformations in 60 cases with asplenia and polysplenia with special reference to distinguishing factors which may be helpful in the clinical recognition of these syndromes. The asplenia cases were predominantly male and presented with cyanosis. They frequently had transposition of the great arteries (72%) with pulmonary stenosis or atresia (88%) and total anomalous pulmonary venous drainage (72%). Deaths were caused by cardiac failure and anoxia in 57 per cent of cases. Most of the patients died in the first year of life (79%), but longer survival is possible in the asplenia syndrome. The polysplenia cases were predominantly female and survived longer. The characteristic clinical findings were the relatively more benign presenting signs and the leftward or superiorly orientated P wave axis on the electrocardiogram. Conotruncal abnormalities were less common and total anomalous pulmonary venous drainage did not occur. On angiography the inferior vena caval drainage via the azygos system was clearly identified and this was present in all cases at surgery. Our study indicated that the cardiac anomalies in polysplenia were less severe than they were in asplenia and therefore the prognosis in the former syndrome is likely to be more favourable. Three families had two affects sibs but no single genetic factor could be identified. The aetiology of these syndromes remains undetermined.