A 54-year-old women with solitary gastric plasmacytoma, Ig M and kappa-light chain type, associated with multisystem autoimmune disease is described. The gastric plasmacytoma developed seven years after the diagnosis of Hashimoto's thyroiditis, primary biliary cirrhosis and Sjögren's syndrome. We speculate that this plasmacytoma developed in association with an immunodeficient and/or immunosuppressed state resulting from multisystem autoimmune disease and therapy.