A 35-year-old male patient clinically characterized by massive proteinuria and hypertension without evidence of systemic diseases is reported. Histological investigation of renal biopsy specimens revealed extensive nodular formations in the mesangial areas in every glomerulus. Light-microscopic examination did not allow discrimination between the glomerular changes found in these specimens and the nodular glomerulosclerosis described in patients with diabetes mellitus. Electron-microscopic examination confirmed the presence of massive, nodular, mesangial expansions consisting of finely fibrillar substances without electron-dense deposits and circumferential mesangial interposition. Immunofluorescent examination showed the deposition of IgG, C3, fíbrinogen and kappa and lambda light chains in mesangial areas, peripheral capillary loops and a part of the nodules. Furthermore, collagen types IV, V, VI and laminin were detected in the nodules. Amyloid was not observed in these nodules. This diagnosis has not been made, and the mechanism of this nodular glomerulosclerosis remains unknown