A case of extramedullary hematopoiesis (EMH) with a massive mediastinal mass in a 72-year-old woman with hereditary spherocytosis is reported. Several cases of EMH have been described in nonsplenectomized adults with hereditary spherocytosis, and it is thought to be a consequence of long-term stimulation of erythropoiesis. The exact mechanism remains controversial. EMH should be considered in the differential diagnosis of an asymptomatic paravertebral mass.