An effort was made to identify all infants born with a congenital cardiac defect in 1981 in Sweden by using four different registries: the Swedish Registry of Congenital Malformations, the Medical Birth Registry, the Registry of Death Certificates, and a specially designed Child Cardiology Registry. All infants diagnosed before the age of one year at one of the five child cardiology clinics in Sweden were reported to the latter registry. This registry, together with the Congenital Malformation Registry, can be used for surveillance as they together cover 85%-90% of all severe cases identified. The data quality in the Medical Birth Registry is too low to permit meaningful surveillance. A total of 853 infants with a diagnosis of a congenital cardiac defect were identified. This represents 9 per 1000 newborns. Many of the cases were dubious, but the diagnosis was stated as probable in 708 (7.6 per 1000); 146 infants died. Cardiac diagnoses were stored in the Child Cardiology Registry and in the Registry of Congenital Malformations as ISC codes. A Monitor Code is described that can be used for grouping and monitoring of diagnoses. Using these codes, data in the Child Cardiology Registry for 1981-1983 were analyzed and epidemiologic information on maternal age and parity, sex rate, and birth weight distribution is given.