Diabetic nephropathy remains a leading cause for end-stage renal disease indicating a failure of current therapeutic strategies. One factor that impairs our ability to make advances has been the inadequacy of most animal models in manifesting advanced diabetic renal disease. Since these animal models develop marked hyperglycemia, one could assume that hyperglycemia is not enough for the development of advanced nephropathy and thereby additional factors are likely involved. Recently, our research group and others have discovered a new mouse model in which diabetes is induced in mice lacking endothelial nitric oxide synthase (eNOS). Diabetic eNOS knockout mice develop severe renal injuries resembling advanced human diabetic nephropathy. This model thereby suggests a key role for reduced nitric oxide levels in the pathogenesis of diabetic nephropathy. In this article, we summarize recent clinical and experimental evidence for the role of eNOS in diabetic nephropathy.