A 36 year-old man had suffered from psoriasis vulgaris for about 25 years. He had received corticosteroids ointment and PUVA therapy with partial response. In 1987, he was diagnosed as having aplastic anemia (AA) and treated with various medications, but failed to respond. He received an allogeneic bone marrow transplantation (BMT) from his histocompatible sister in 1993. Conditioning regimen of BMT consisted of total lymphoid irradiation (7.5 Gy) and cyclophosphamide (200 mg/kg). Cyclosporin A and methotrexate were given for prophylaxis of graft-versus-host disease. On day 24, bone marrow examination disclosed normocellular marrow and karyotypic analysis completely confirmed the donor's origin. Before BMT, he had systemic psoriatic plaques with scales, together with nail involvement. After BMT, psoriatic plaques disappeared and nail deformity improved. He has remained in remission of his AA and completely free of psoriasis in the absence of immunosuppressive or other treatments. The cause of psoriasis is thought to be an immune-mediated disorder. Our case supports the observation that changing the host's immune system through allogeneic BMT can achieve remission of psoriasis. It is suggested that allogeneic BMT may be one strategy for the treatment of intractable immune-mediated disorders.