The infant mortality from cardiovascular malformations in a region with a population of 2 million inhabitants during a 10-year period has been studied. The study involved validation of the diagnoses and judgement whether the cardiovascular malformation was the dominating or a contributing cause of death. It is shown that the incidence of fatal cardiovascular malformations is probably overestimated in the official death statistics. Evaluation of the clinical findings and necropsy reports are important aids in obtaining more reliable figures of the incidence. The rate of referral of infants with cardiovascular malformations has increased during the period of this study, so that the number of operable lesions not referred has decreased. The infant mortality rate, found in this study, of 1.33 per 1000 liveborn babies constitutes about 20 per cent of all liveborn infants with cardiovascular malformations. The most common lesions found in those who died belonged to the group constituting the hypoplastic left heart syndrome. The proportion of this type of malformation, about 20 per cent of all those dying, is higher than in other similar studies. This difference can probably be explained by variations in selection and classification.