Acute febrile neutrophilic dermatosis, or Sweet's syndrome, usually occurs in middle-aged women with a preceding upper respiratory tract infection. In about 20 percent of reported cases, the syndrome is associated with an underlying malignancy, most frequently acute myelogenous leukemia. A dense infiltrate of mature neutrophils is seen in the middle and upper portions of the dermis. Corticosteroid therapy produces rapid improvement of all manifestations of the syndrome.