A seventy-six-year-old woman with plasmacytoma presenting as a renal mass died three months after diagnosis. Bone surveys disclosed no lytic lesions. Gallium-67 scan showed an avid uptake of the radionuclide in the renal mass. Histologic and immunofluorescence studies of resected specimens demonstrated that the renal parenchyma was destroyed by sheets of immature plasma cells producing IgM-lambda and by massive deposits of amorphous, eosinophilic substance stained with anti-mu and anti-lambda antisera. The literature is reviewed. We believe this case is the first one of well-documented IgM-producing renal plasmacytoma.