Diabetic nephropathy is a leading cause of end-stage renal disease in Japan. Microalbuminuria has been considered as the first clinical sign of diabetic nephropathy. However, recent studies demonstrated that normoalbuminuric renal insufficiency is not uncommon for diabetic patients, especially in type 2 diabetes. Although the pathogenesis of normoalbuminuric renal insufficiency in diabetic nephropathy remains to be fully elucidated, distinct clinical and pathological features of diabetic patients with this finding have been reported as compared to those in diabetic patients with a typical clinical course. In type 1 diabetes, more advanced glomerular lesions were found in patients with normoalbuminuric renal insufficiency than in patients with normoalbuminuric preserved renal function. In contrast, disproportionately advanced tubulointerstitial and vascular lesions, despite minor diabetic glomerular lesions, which denote the presence of diabetic kidney lesions as well as nephrosclerosis, were likely to be related to the development of normoalbuminuric renal insufficiency in some type 2 diabetic patients. In addition, long-term outcomes of diabetic patients with normoalbuminuric renal insufficiency remain controversial. Further studies to gain a better understanding of the structural-functional relationships and natural history of diabetic patients with normoalbuminuric renal insufficiency may improve the benefits of therapeutic interventions for diabetic nephropathy.