The paper describes a case of generalized lymphadenopathy clinically recognized as malignant lymphoma in a 59-year-old woman. Her death occurred from bilateral pneumonia. Autopsy also showed a tumor-like mass in the thymus. On histological examination, the lymph nodes, thymus, and spleen exhibited an intensive polyclonal IgG4+ plasma cell infiltration. Lymphoid plasma cell infiltration with increased count of IgG+ plasma cells, progressive sclerosis, and phlebitis obliterans were found in the pancreas and peripancreatic adipose tissue, liver, kidney, epicardium, thyroid, pituitary, skin, and other organs. The case was regarded as IgG4-related sclerosing disease manifesting itself as lymphadenopathy and thymus enlargement.