Direct revascularization has been used successfully to prevent strokes by improving regional cerebral blood flow (rCBF) to the affected hemisphere faster in patients with moyamoya disease (MMD). Since most literatures have focused on the rCBF changes of operative hemisphere, we evaluated the hemodynamics of nonoperative side by xenon-enhanced computed tomography (Xe-CT) and acetazolamide challenge test in patients with MMD during a short time follow-up. Fifteen MMD patients with unilateral ischemic presentations who received direct revascularization on the symptomatic hemispheres with complete hemodynamic evaluations by Xe-CT and acetazolamide challenge test were enrolled. Hemodynamic evaluations were performed 1, 3, and 6 months, postoperatively. The postoperative rCBF and cerebral vascular reserve (CVR) were recorded and correlated with clinical outcome. Angiography was performed if the patient had neurological deterioration or deficits. The average follow-up time was 8.5 +/- 3.5 months. Three months after the ipsilateral direct revascularization, the CVR of nonoperative hemispheres (25.8 +/- 8.1%) began to decrease significantly (P = 0.003). Six months later, the rCBF showed a downward trend in nonoperative hemispheres (47.4 +/- 8.0 ml center dot 100 g(-1) min(-1)) than the preoperative status, but the difference was not significant (P = 0.053). Three patients presented with decreased rCBF and impaired CVR in the nonoperative hemispheres. Among them, two patients were symptomatic. Unilateral direct revascularization in symptomatic hemisphere for MMD patient could induce CVR impaired in primary asymptomatic hemisphere during the short term after the surgery. Therefore, critical follow-up, especially the hemodynamic follow-up in the asymptomatic hemispheres should be performed in patients with MMD.