Multicentric reticulohistiocytosis (MRH) is a rare disease affecting joints, skin and internal organs. Yet the cause is still unknown. In most cases, it can be misdiagnosed as rheumatoid arthritis or psoriatic arthritis before typical change in the skin emerges, and precise diagnosis is essential because it may become severe enough to transform and destroy the joints. Therefore, skin or synovial biopsy can confirm the existence of this disease. This particular patient is a 39-year-old male who had been treated for rheumatoid arthritis on a wrist and hand and transferred to this hospital when arthritic pain continued with erythematous papules and nodules on the hands, the outer rims of the ears, hands and elbows. The X-ray examination of both hands revealed multiple marginal erosion of proximal and distal interphalangeal joints and destruction of subchondral bones. periarticular osteoporosis and joint space enlargement is combined, but no new bones were seen to be formed. Biopsy of erythematous nodules on the dorsum of hands showed that an infiltrate histiocytes and multi-nuclear giant cells were aligned irregularly, and immunological chemical staining showed potential for being positive to PAS and CD68. To control pain and regulate activity of the disease, tracing observation and treatment were started from the outside with NSAID, hydroxycholoquine, MTX and prednisolone. A month of treatment did not improve arthritis and skin problems, and increased dose of MTX, prednisolone did improve arthritis a little but not skin problems. Treatment with infliximab (3

mg/kg), a anti-tumor necrosis factor, is in progress, showing improvement in both conditions.