The mediastinum is seldom involved by granulocytic sarcoma and superior vena cava (SVC) obstruction is an even rarer presentation. Some radiologists advocate to treat SVC obstruction as a semimedical emergency regardless of the underlying pathology. This policy has been criticized. We describe a patient with severe SVC obstruction preceding the development of frank acute myeloblastic leukemia and granulocytic sarcoma in breasts. Review of the literature yields 11 patients with prominent mediastinal granulocytic sarcoma complicating myeloid leukemia; 3 of them presented with superior vena cava syndrome.