We report the case of a 46-yr-old man with a 16-yr history of type I diabetes mellitus who developed rapid onset of nephrotic syndrome. Renal biopsy revealed diabetic nephropathy, characterized by thickened glomerular basement membranes (GBM), mild nodular glomerulosclerosis, and focal arteriolar hyalinization. Immunofluorescent (IF) studies showed strong granular IgM staining along glomerular loops, with subepithelial and intramembranous immune complex deposits along glomerular capillary loops demonstrated by electron microscopy (EM). These findings are consistent with membranous glomerulopathy with IgM as the predominant immunoglobulin. In addition, there were large aggregates of electron-dense material composed of numerous ring or spherical particles, ranging from 200 to 400 nm, in Bowman's space, which corresponded to eosinophilic aggregates on light microscopy (LM) and strong IgM stained materials by IF studies.