Granulocytic sarcoma is a rare orbital complication of acute leukemia. It concerns primarily children under 10 years of age suffering from primitive acute myeloid leukemia. As this type of symptom can sometimes affect the elderly during the acute phase of myelodysplastic syndrome, it raises a problem with diagnosis and consequently with therapeutic treatments. We report the case of a 77-year-old female patient who had acute inflammatory proptosis during regressive right ethmoiditis. The diagnosis was reached by computed tomography showing an extraconical intraorbital tumor sprouting from the sinus, and by clinical examination and confirmed by the hematological investigation. Acute proptosis developing in an acute myeloblastic leukemia context heavily swayed diagnosis towards orbital granulocytic sarcoma. Chemotherapy by cytarabine and hydroxycarbamide associated with intravenous corticoid therapy resulted in complete disappearance of the proptosis within 10 days. This case report is a reminder of this peculiar sign of tumoral syndrome in acute myeloid leukemia. We also discuss different diagnostic methods and various therapeutic approaches, and analyze the disease course and patient follow-up.