A case of Sweet syndrome in a patient with an acute myelomonocytic leukemia is reported. It is an unusual case simulating a facial erysipela. This case illustrates the difficulty in differentiating infection from Sweet syndrome in an immunocompromised patient. The negative cultures, ineffective antibiotics, and histopathologic examination results allowed the onset of corticosteroid therapy. The phagocytic function of the neutrophils studied by chemoluminescence was normal in the patient. The physiopathology of Sweet syndrome is discussed, in particular the role of cytokines in the accumulation of granulocytes.