A long-term follow-up study of diabetic patients was carried out in Osaka, Japan. The subjects were 1,850 diabetics, who were first seen at our hospital between 1960-1979, and they were followed up until the end of 1980. Both the mean annual mortality rate and the O/E ratio indicated an excess mortality in diabetic patients compared to the general population, and a higher mortality in males than in females. Factors related to the prognosis of the subjects were elevated systolic blood pressure, albuminuria and elevated fasting glucose levels at the baseline, and poor metabolic control and insulin treatment during the follow-up period. Cerebrocardiovascular and renal diseases accounted for nearly half of all deaths. When compared to the expected death rate, the increase in the number of deaths due to renal disease was remarkable. Malignant neoplasms also exhibited an increase in the O/E ratio, and were responsible for one quarter of all deaths. In particular, an increase in cancer of the liver and of the pancreas was noted. In addition, an increased O/E ratio was observed for cirrhosis of the liver.