The incidence of significant extracardiac malformations was determined in a combined clinical and autopsy study comprising 1000 infants and children with congenital heart disease treated and lost at the Children's Hospital in Helsinki. There were 567 boys and 433 girls. 1/4 of the children had a birthweight of 2500 g or less. 850 children were under 1 yr old. Death occurred during the 1st mth of life in 546 cases. Extracardiac malformations were encountered in 439 children. They were more common in girls than in boys. The incidence of associated malformations was comparatively high in infants with a low birthweight. The noncardiac anomalies were considered main causes of death in 1/3 of the cases. Extracardiac organs were involved in the following order of frequency: alimentary, skeletal, urogenital, central nervous and respiratory system. Of the main cardiac malformations, septal defects were associated with the highest and transposition of the great arteries with the lowest incidence of extracardiac anomalies. An accumulation of some defined noncardiac malformations was observed in patients with certain heart lesions.