A case of a small amount of IgG λ M component, chronic progressive polyneuropathy, primary hypothyroidism, diabetes mellitus, elevated serum estrogen level, gynecomastia, impotence, generalized lymphadenopathy, peripheral edema, hirsutism, pigmentation and thickening of the skin, slight fever, and excessive perspiration is reported. Five similar cases, all in Japan, are known, and a new syndrome of plasma cell dyscrasia, polyneuropathy, and endocrine disturbances has been suggested recently by other researchers. We think that our case is the sixth case of this syndrome. The pathogenesis of this syndrome is unknown, but some genetic or racial factor may contribute to it.