Muscle involvement in acute febrile neutrophilic dermatosis is uncommon. Herein, we report a case of acute febrile neutrophilic myositis, without cutaneous involvement, as the first manifestation of acute myeloid leukemia. The patient was a 35-year-old male, referred due to painful swelling of the left upper arm and fever. The overlying skin looked normal, and a muscle biopsy revealed dense infiltrates, predominantly composed of mature neutrophils, edema and tissue necrosis. All culture reports were negative, and he was finally diagnosed as having acute febrile neutrophilic myositis, associated with acute myeloid leukemia. Corticosteroid treatment resulted in the progressive regression of the fever, myalgia and swelling.