A 53-year-old Japanese man with multiple sclerosis developed autoimmune neutropenia. The neutrophil count was consistently less than 0.2 x 10(9)/l, irrespective of the disease activity of multiple sclerosis or the administration of immunosuppressive agents or granulocyte colony-stimulating factor. After high-dose gamma-globulin therapy was started, temporary increases in the neutrophil count were observed. Despite a wide spectrum of clinical manifestations in multiple sclerosis, autoimmune neutropenia has never been reported previously.