Natural killer leukemia is a rare and highly aggressive neoplasm, is more common in young male patients and has a very poor prognosis, with a median survival of few weeks. We report a 17 years old male patient who developed, after an acute upper respiratory disease, a rapidly multiorganic failure with pancytopenia. Bone marrow aspiration and trephine biopsy showed an acute lymphoblastic leukemia. The immunophenotype and immunohistochemistry revealed a natural killer acute leukemia. The disease progressed rapidly and the patient died shortly after the diagnosis