We described the case of a thalassemic woman who underwent splenectomy three decades ago, and complained of shortness of breath that progressively worsened. Chest computed tomography and magnetic resonance imaging revealed a 3×3 cm mass over the posteroinferior mediastinum, and the mass was suspected to be extramedullary hematopoiesis (EMH). A Gallium-67 tumor survey showed no abnormal uptake over this mass. Tc-99m sulfur colloid bone marrow scintigraphy revealed a focal hot area in the right posteroinferior mediastinum adjacent to the T-spine, suggesting EMH. According to the diagnosis of noninvasive radionuclide scanning, the patient underwent a suitable management without taking the risk of a biopsy.