A new syndrome has been described comprising polyneuropathy, oedema, hyperpigmentation and thickening of the skin, gynaecomastia in males and amenorrhoea in females, monoclonal gammopathy, papilloedema and diabetes. There is frequent osteosclerosis with or without plasmacytoma, hepatosplenomegaly and polycythaemia. There is a good response to corticosteroids, immunosuppressive drugs and occasionally to excision or irradiation of the plasmacytoma. This syndrome was first described in Japan, and is still seen predominantly there, and only occasionally in other areas. An example in a 51-year-old Spanish female is described: she had a spectacular response to prednisone and melphalan. The aetiopathogenic possibilities are discussed.