The causes of death in 130 patients with Down's Syndrome and mortality rates from a material of 524 patients were tabulated; a life-table for the ages over 5 years was constructed. An overall death rate of 5-7 times the general population rate was found. No sex difference was observed. The excess mortality was expecially high for heart disease and respiratory disease. Also infectious diseases, others than pneumonia and tuberculosis, showed high mortality rates.