BACKGROUND the association of acute febrile neutrophilic dermatosis (Sweet's syndrome) with malignant haemopathies is well known and characterized by an usual lack of hyperleukocytosis: indeed, moderate neutropenia is often reported. However, cases of Sweet's syndrome in the agranulocytosis stage are exceptional (7 in the literature). METHODS We report the case of a woman with acute myeloblastic leukaemia who had presented with Sweet's syndrome in the phase of therapeutic aplasia during induction of treatment, in the absence of white blood cells transfusion or treatment with haematopoietic growth factor (GM CSF, GCSF). CONCLUSIONS the physiopathology of Sweet's syndrome is unknown. Various mechanisms have been suggested, including immune reaction type III, increased interleukin-1 synthesis, increased chemotaxis of neutrophils, action of haematopoietic growth factors, iatrogenic effect of some drugs (e.g. cotrimoxazole, furosemide or minocycline). Yet none of these mechanisms involving circulating polymorphonuclears or their bone marrow precursors can explain the occurrence of Sweet's syndrome in the phase of agranulocytosis. CONCLUSIONS the diagnosis of Sweet's syndrome must be considered in patients with agranulocytosis in order to avoid ineffective antibiotics and to initiate a corticosteroid therapy that will accelerate the cure of this benign dermatosis.