OBJECTIVE: To use territory arterial spin labeling (T-ASL) in the early postoperative period to evaluate the revascularization area (RA) obtained by superficial temporal artery-to-middle cerebral artery bypass and to evaluate subsequent perfusion territory changes of the major cerebral arteries. METHODS: Thirty patients with moyamoya disease treated via unilateral superficial temporal artery-to-middle cerebral artery bypass were included. T-ASL was performed preoperatively and within 1 week postoperatively. The RA was examined by labeling the superficial temporal artery-to-middle cerebral artery bypass postoperatively. Preoperative and postoperative perfusion territories of the bilateral internal carotid arteries, bilateral external carotid arteries, and basilar artery were also examined and compared. Postoperative computed tomography angiography was performed and compared with T-ASL results. RESULTS: In 14 of 30 patients (46.7%), T-ASL demonstrated the presence of an RA (RA-positive), whereas 16 patients (53.3%) had no RA (RA-negative). In the RA-positive group, mean volume of the RA was 80.32 +/- 8.13 mL (range, 34.95-142.50 mL). Postoperative perfusion territory changes of the major cerebral arteries differed between the RA-positive group and the RA-negative group. The incidence of preoperative external carotid artery compensation was significantly higher in the RA-negative group than the RA-positive group (F = 0.011, df = 1, P < 0.05). There was good intermodality agreement between T-ASL and computed tomography angiography (kappa = 0.780). CONCLUSIONS: T-ASL can demonstrate the RA obtained by direct revascularization and postoperative perfusion territory changes of the major cerebral arteries. T-ASL is a promising technique in postoperative evaluation of patients with moyamoya disease.