A 46-year-old man diagnosed as refractory anemia was hospitalized because of high fever and extensive erythema with ulceration in the femoral region. His peripheral blood examination showed marked leukocytosis (WBC 31,500/microliter:neutrophilic 90%) and anemia (Hb 8.6 g/dl. In spite of administration of antibiotics, the cutaneous ulcer rapidly extended to the right thigh and became necrotic. The bacterial culture of the cutaneous lesion showed no growth and a skin biopsy showed infiltration of neutrophils in the dermis. He became afebrile and his cutaneous lesion improved after administration of corticosteroid. When the dose of corticosteroid was decreased, cutaneous erythema and nodules appeared at other sites repeatedly, and disappeared after the dose of corticosteroid was increased. The cutaneous lesions had characteristics of both Sweet's syndrome and pyoderma gangrenosum. Moreover, the patient had immunological abnormalities and decreased neutrophilic functions (chemotaxis and O2- generation). Thus, it was suggested that the cutaneous lesions of this patient could be diagnosed as "neutrophilic dermatosis of MDS", and corticosteroid was recognized to be very effective in treating these skin lesions.