Down's syndrome (DS) is the most common form of intellectual disability. The syndrome is characterized by congenital malformations, especially of the heart and gastrointestinal tract, which can result in high mortality rates in the affected population. Many improvements have been made in the medical treatment of this syndrome during the past few decades and the survival of individuals with DS has increased in the industrial world. The aim of the present study was to investigate mortality in relation to congenital malformations. Medical records from all liveborn children with DS delivered between 1973 and 1980 in northern Sweden were studied, and malformations and causes of death were recorded. Out of the 219 children included in the study, a congenital heart defect was reported in 47.5% of subjects, 42.1% of whom had complete atrioventricular septal defect. Gastrointestinal tract malformations were present in 7.3% of subjects, and was frequently associated with a cardiac malformation and a very high mortality rate. Other major and minor congenital anomalies were present in 5.5% and 5.5% of subjects, respectively. In the 14.5-year follow-up of 213 children, the rate of survival was 75.6%. Mortality rates within one and 10 years after birth were 14.6% and 23.5%, respectively. Mortality within 10 years differed significantly between children with (44.1%) and without (4.5%) a congenital heart defect. A very high mortality rate was observed among children with a congenital heart defect, especially when it was combined with a gastrointestinal malformation.