The clinicopathological and laboratory findings for 35 diabetic patients who had undergone renal biopsy from 1982 to 1990 were reviewed. Ten of these patients (28.6%) were found to have nondiabetic renal diseases. Five of those patients (14.3%) suffered from nondiabetic renal disease complicated by diabetic nephropathy. Nondiabetic renal diseases included IgA nephropathy, idiopathic membranous nephropathy, membranoproliferative glomerulonephritis (types I and III), minimal change disease, and toxemia of pregnancy. The diagnosis of nondiabetic renal diseases complicated by diabetes is important for the treatment of renal disease. Urinary abnormalities and/or deterioration in renal function inconsistent with the natural history of diabetic nephropathy were suggestive of the presence of nondiabetic renal disease.