A 73-year-old male was admitted in January 1999 with hyperimmunoglobulinemia with a serum IgG level of 6530 mg/dl, bilateral eyelid tumors, bilateral submandibular swelling, and swelling of the superficial lymph nodes. A left submandibular gland biopsy showed severe chronic sialoadenitis with fibrosis. A left cervical lymph node biopsy showed invasion by many mature lymphocytes and plasma cells, but no lymphoma cells. The patient was diagnosed as having so-called Mikulicz disease associated with a disease similar to multicentric Castleman disease (MCD) characterized by multicentric lymphadenopathy and polyclonal hyperimmunoglobulinemia. Steroid therapy (prednisolone, 20 mg/day) was effective in reducing the symptoms, the bilateral eyelid tumors and the swelling of the bilateral submandibular glands and superficial lymph nodes. The lack of any increase of serum IL-6 suggested that this case had a hitherto unknown etiology, other than MCD.