OBJECTIVE: To evaluate blood flow changes after bypass surgery for refractory symptomatic intracranial atherosclerotic stenosis (ICAS). METHODS: We examined a cohort of consecutive patients with symptomatic ICAS. Superficial temporal arterye middle cerebral artery (MCA) bypass was performed in refractory patients with poor perfusion. Angiograms were graded systematically for antegrade, collateral, and bypass flow, and clinical variables were collected preoperatively, at 7 days postoperatively, and 3, 6, and 12 months postoperatively. RESULTS: Among 185 consecutive cases with ICAS, 15 patients who were unsuitable for or did not respond to the best medical therapy or stenting underwent bypass surgery. No patients had new ischemic deficits within 7 days postoperatively. The mean follow-up period was 30.2 +/- 12.3 months. Within this period, all anastomoses were patent by methods of ultrasound or computed tomography angiography. In 2 patients, stenotic lesions exhibited early postoperative occlusion conversion at 7 days on digital subtraction angiography. In 2 patients, stenotic lesions showed progression of occlusion at 6 and 8 months. The 2 lesions with early occlusion were both located in the MCA. The extent of retrograde blood flow via bypass anastomosis was correlated with early occlusion conversion. CONCLUSIONS: For refractory ICAS in patients with compromised hemodynamics, direct bypass might induce early occlusion of a stenotic area. MCA lesions may have a greater tendency toward early occlusion conversion.