Granulocytic sarcoma (GS) is a solid tumor of extramedullary localization constituted by immature precursors from the granulocytic series. GS may be diagnosed in different malignant blood diseases involving the granulocytic series, acute non lymphoblastic leukemia (ANLL) being the most frequent, followed by myelodysplastic syndromes (MDS) and chronic myeloproliferative syndromes, specially chronic myeloid leukemia (CML) in blastic crisis. Although the diagnosis of GS is suspected with conventional cytologic and anatomopathologic studies, histochemical staining and immunohistochemical techniques are often required for definitive diagnosis. Five cases (4 males, 1 female; age range 22-77 years) diagnosed with GS in one center over a period of nine years (1984-1993) are described. The GS were located in the lymph nodes, the jaw, paravertebral region, gallbladder and retroperitoneum, respectively. Two patients had refractory anemia with excess of blasts (RAEB). Three patients had ANLL; in one GS constituted the form of relapse, in another GS presented at the time of diagnosis and in the remaining patient GS preceded the diagnosis of ANLL. All the patients died from 2 to 8 months after diagnosis of GS with no response to treatment being observed. Immunohistochemical study of the tumor was performed in 4 patients, being positive for lysozyme and the monocytic MAC-387 monoclonal antibody. Immunocytochemical study of the tumor blasts was carried out with positivity for CD15 being observed. Although uncommon, GS should be suspected in patients with ANLL or MDS with tumors of any localization and at any time during its evolution. Immunocytochemical and immunohistochemical studies are of great value to differentiate GS from other tumors, particularly anaplastic non Hodgkin's lymphomas.