A 32-year-old Japanese male presented with abundant proteinuria, and renal biopsy revealed diffuse subendothelial and mesangial deposits in the glomeruli without hypercellularity or mesangial interposition. There was no clinical or laboratory evidence of systemic conditions such as collagen-vascular disease, paraproteinemia, or infection. Treatment with corticosteroid was ineffective and the patient eventually went into end-stage renal failure. To our knowledge, this is the first report of an idiopathic progressive glomerulopathy characterized by diffuse, global subendothelial and mesangial deposits, which suggests to us a novel insight into glomerular subendothelial/mesangial deposition.