Intrathoracic extramedullary hematopoiesis rarely involves the pleura and is usually asymptomatic. We report a 73-year-old woman with myelofibrosis who had pleural involvement with extramedullary hematopoietic tissue that produced a massive hemothorax. Before the diagnosis of extramedullary hematopoietic tissue was established, sclerosis with tetracycline was attempted, which accelerated pleural bleeding and required surgical evacuation. The bleeding was ultimately controlled by low-dose radiation therapy.