A 61-year-old woman with rheumatoid arthritis (RA) developed small digital ulcers, proteinuria, and hematuria. Serological studies disclosed high titers of antinuclear antibody and rheumatoid factors (RF; IgM-RF and IgG-RF), and an increased level of circulating immune complexes. These findings suggested an active immunological state of RA. A renal biopsy showed periodic acid-Schiff-positive giant deposits in the mesangial area and subepithelial space. Immunofluorescence microscopy revealed strong stainings for IgG, IgA, IgM, Kappa, Lambda, C3, C1q, and fibrinogen in a granular pattern. Electron microscopy showed giant granular deposits (diameter, up to 4.6 micro m) without specific fibrillary structure in the mesangial area and subepithelial space, and partially in the subendothelial space. There were no findings of vasculitis, such as endothelial proliferation or fibrinoid necrosis of small arteries. This is the first report of immune complex-type glomerulonephritis with unusual giant deposits in a patient with RA in an active immunological state.