Background: Visceral obesity and metabolic syndrome have been proposed as major coronary risk factors, however non-obese diabetes patients have also significant coronary atherosclerosis. Purpose: To elucidate the difference of prognosis between obese diabetes and non-obese diabetes. Methods: Up to December 2003, 606 patients who were initially treated with PCI, were recruited as cohort, and followed up for mean 10.3 years. Patients were divided into four groups according to diabetes and obesity. Endpoints are occurrence of new coronary lesions. Results: Non-obese diabetes had more frequently new coronary lesions than obese diabetic patients, indicating the incidence rate at 10 years was 56% and 31%, respectively (p=0.0017). At baseline, frequency of chronic kidney disease (CKD) was almost equal in these two groups, however, during follow-up, percentage of death associated with renal failure significantly increased up to 21.4% in non-obese diabetes, whereas 4.4% in obese diabetes. This increase is coincidence with occurrence of new coronary lesions, indicating diabetic microangiopathy is strong promoting factor in pathogenesis of coronary atherosclerosis in non-obese diabetes. Conclusion: In lean diabetes, microangiopathy especially nephropathy are frequently occurred, and this may contribute to progression of coronary atherosclerosis via the same mechanisms such as oxidative stress and glycation endproducts, or indirectly via secondary hypertension. these intriguing interaction of microangiopathy and macroangiopathy make unique coronary anatomy observed in diabetes.