The hearts of 291 babies with congenital heart disease who died before the age of one were examined systematically by sequential segmental analysis to determine the lesions that were present. There was an abnormal connection between the cardiac segments in one third of cases. Patient ductus arteriosus, which is usually a common defect, was not an important finding at necropsy, whereas common arterial trunk (a rare defect) was found in 10%. The clinical and necropsy incidence of complete transposition was similar to that reported in earlier studies. The incidence of some lesions present at necropsy (for example Fallot's tetralogy) has altered over the past 10 years. A decline in the frequency with which a lesion is detected at necropsy may indicate advances in treatment or differences in classification. The presence of additional lesions influences the prognosis and subcategorisation within the major defect groupings gave some insight into the cause of death in many of the cases.