Myeloid sarcoma or granulocytic sarcoma (GS) is a rare disease with poor prognosis. It is characterized by the occurrence of tumor masses at an extra-medullary tissue. It is composed of myeloblastic cells and usually occurs in association with acute myeloid leukemia. Because of its nonspecific clinical and radiologic findings, its diagnosis might be challenging. It might be more commonly found in patients with specific cytogenetic abnormalities, particularly with the t (8; 21) translocation and less frequently the inv (16) type. We report a case of GS in a 62 years old man without particular previous pathologies, which brutally presented as an ascites and generalized edema. The laparoscopy showed involvement of greater omentum and peritoneum. The histologic examination of greater omentum showed granulocytic sarcoma. The bone marrow aspiration was normal. We started treatment of patient by standard acute myeloid leukemia's chemotherapy.