The influence of obesity on the development of ischemic heart disease (IHD) was studied in 103 diabetic patients over 65 years of age. The patients were divided into three groups on the basis of their body mass index: lean, less than 20; normal, 20-25; obese, greater than 25. The incidence of IHD was significantly (p less than 0.01) higher in the obese group than in the other groups (43.2 vs. 18.8 and 16.3%). The age, sex distribution, duration and control of diabetes mellitus, methods of diabetic therapy, and prevalence of hypertension, hyperuricemia and smoking were not significantly different in the three groups. The level of serum triglyceride was higher and that of high-density lipoprotein cholesterol (HDL-C) was lower in the obese group than in the other groups, but the prevalence of IHD was significantly higher in the obese patients without hypertriglyceridemia and/or low HDL-C than in the normal group (p less than 0.05). These results suggest that obesity is a risk factor for development of IHD in elderly diabetic patients independently of other known risk factors.