To clarify the characteristics of diabetic nephropathy (DN) in Japanese patients with non-insulin-dependent diabetes (NIDDM), we analyzed the clinical course of 130 such patients who began dialysis treatment due to DN between 1978 and 1988 at the Diabetes Center of Tokyo Women's Medical College. Analysis of the clinical course prior to attending the Diabetes Center revealed that 64 (49.2%) of the patients neglected or discontinued their initial treatment for diabetes until the development of diabetic complications because of the lack of symptoms. The average duration of untreated diabetes in these patients was 10.7 +/- 4.6 years. The biggest problem for NIDDM patients was the absence of symptoms until the development of diabetic complications.