The granulocytic sarcoma is a rare and extramedullary tumor, which is composed of granulocytic precursor cells. The diagnosis remains difficult. Infectious disease are often associated with leukemic processes. Combination of clinical, radiological and pathological findings are useful for diagnosis. On gross examination, the tumor appears green. The detection of myeloperoxidases and the presence of immature eosinophils can help histological analysis. Granulocytic sarcoma occurs before or during an acute leukemia. It is treated like an acute leukemia. Prognostic is greatly improved by early diagnosis and treatment. The lack of cytogenetic abnormalities is associated with a prolonged survival. We describe a new case of rapidly growing pleural granulocytic sarcoma. The uncommon modifications of chromosome 5 long arm in this case could explain the immature eosinophil reaction in that tumor.