- Abstract: Obstructive sleep apnea can be caused by hypertrophy of tonsils and adenoids or neuromuscular diseases. The authors describe a child with thalassemia intermedia in whom severe obstructive sleep apnea syndrome developed. Computed tomography scanning revealed an obstruction of the nasopharynx resulting from extramedullary hematopoiesis. The child was treated with hydroxyurea and blood transfusions. Relief of symptoms was noted 1.5 months after initial treatment. Extramedullary hematopoiesis causes sleep apnea syndrome in thalassemic patients, and the treatment of hydroxyurea and blood transfusion for extramedullary hematopoiesis should be further studied.