The incidence of congenital heart defects (CHD) in a birth cohort of 12,058 live births born in Northern Finland in 1966 was 4.15/1000 with a mortality due to CHD 1.41/1000 up to 14 years of age. The long-term social and educational outcome for CHD children was significantly poorer than for normal children of the same age when evaluated on the basis of school and army service records, and the incidence of cerebral palsy, epilepsy and mental retardation was significantly higher. 15.4% of the Down's syndrome cases in the cohort also had CHD. The CHD boys were significantly lighter in weight than the controls even as adolescents (14 years of age). The only difference between the operated and non-operated group was the higher weight of the boys at the age of 18 years in the former.