Between January 1976 and December 1987 42 children with Down syndrome and congenital heart disease underwent cardiac surgery. Four children had two operations. Age at the time of surgery ranged from 11 days to 14 years. The commonest operative procedure was repair of a patent ductus arteriosus. Four patients died post-operatively, two following repair of a complete atrio-ventricular canal defect (CAVD), one following correction of tetralogy of Fallot in association with a CAVD, and a fourth following closure of ventricular septal defect and atrial septal defect. The mortality for those who had open heart surgery was 13.3% and for the series as a whole the mortality was 6.6% over a period of follow-up ranging from two months to four years. A relatively conservative approach has been adopted with regard to surgery, based on the shorter natural expectation of life in Down syndrome, the complexity of many of the cardiac lesions involved and the recognition of the frequency of early intellectual deterioration in Down patients.