The present study described 3 patients with idiopathic membranous glomerulonephritis associated with diabetes mellitus. Clinical characteristics of the 3 patients contrasted with diabetic glomerulosclerosis in the following manner: absence of diabetic retinopathy and neuropathy, and presence of nephrotic syndrome associated with relatively short duration of diabetes mellitus. Renal histology showed the characteristic changes of membranous glomerulonephritis along with those of diabetic glomerulosclerosis. Immunofluorescent studies demonstrated a granular pattern of IgG and C<sub>3</sub> deposits along the glomerular capillary wall. Electron microscopic study also demonstrated thickening of glomerular basement membrane and increase of mesangial matrix as well as the presence of electron-dense deposits primarily in the subepithelial and mesangial areas.