The incidence of congenital heart disease (CHD) has been shown to be 0.8-1.0% and of these 0.5% will require specific treatment. An investigation on Icelandic children born 1985-1989 showed a slightly higher incidence or 1.1%. Iceland is well suited for population studies because investigation, treatment or treatment decision are made centrally, the population is stable and the country geographically well defined. The purpose of our study was to investigate the number of Icelandic children who required cardiac surgery because of CHD, the distribution between specific defects, the number of operations, age at first operation, mortality and causes of death. The study deals with children born in Iceland from 1969 to 1993 that had been operated upon for CHD during the period January 1st 1969 to May 1st 1994. Data were collected from the Departments of Pediatrics, Surgery and Medicine of Landspitalinn, National University Hospital. During this 25 year period 299 children had 354 operations because of CHD or 2.75 per 1000 livebirths. The mean age at operation has fallen from 4.7 years in 1969-1973 to 0.8 years in 1989-1993. Operations done in England were 261 and 79 in Iceland. The most commonly encountered defect was ventricular septal defect (VSD). During the study period the frequency of operations for the individual defects was stable except for atrial septal defect (ASD) which increased after 1984. Of the 299 children 31 are dead (10.4%). Of 1000 live born children 2.75 will require cardiac surgery because of CHD. The reason for reduced age at operation and increasing operation frequency for ASD are probably because of better diagnostic technique and improved knowledge about the disease process.