Objective To investigate the clinical features, pathogenesis and treatment effects of patients with moyamoya syndrome associated with hyperthyroidism. Methods The clinical data of 10 patients with moyamoya syndrome associated with hyperthyroidism from department of neurosurgery were analyzed retrospectively. These patients were diagnosed MMS by magnetic resonance angiography (MRA) or digital subtract angiography (DSA). All the patients met the diagnostic criteria of hyperthyroidism. After controlling hyperthyroidism, 9 patients underwent encephalo-duro-arterio-synangiosis, the other 1 was only given drugs to control hyperthyroidism. Results 10 patients (7 females) showed thyroid dysfunction. 2 patients showed high level of immunoglobulin. 4 patients showed high level of antinuclear antibody spectrum. 10 patients showed cerebral infarction by CT or MR and all patients had bilateral lesions. After controlling hyperthyroidism, 9 patients underwent encephalo-duro-arterio-synangiosis, the other 1 was only given drugs to control hyperthyroidism. 10 patients were followed-up for 5～48 months. The symptoms of 9 patients were relieved or disappeared after the treatment. 8 of them conducted postoperative DSA (12～24 month) and all showed a great deal of compensatory blood supply from extracranial to intracranial arteries. Conclusion Moyamoya syndrome associated with hyperthyroidism is mostly occurred in female patients and their clinical symptoms are mainly cerebral infarction. The pathogenesis of moyamoya syndrome associated with hyperthyroidism may be associated with a variety of genetic and immune factors. After controlling hyperthyroidism, encephalo-duro-arterio-synangiosis is thought to be an appropriate management for prevention further ischemic stroke.