Using 133Xe single photon emission tomography, we evaluated the cortical region cerebral blood flow (rCBF) and vascular response to acetazolamide loading before and after vascular reconstructive surgery in 9 hemispheres in 6 patients with adult-onset moyamoya disease. Before the operation, the resting rCBF was not markedly impaired except that several low rCBF regions were present in the frontal and temporal lobes, and after the operation, the number of regions showing normal rCBF was significantly increased. Regional vascular response was more diffusely impaired in the regions with both normal and low rCBF before the operation, the excessively high response observed in the parietal and occipital lobes was well normalized after the operation, while the low response to acetazolamide challenge in the frontal and temporal lobes was not adequately improved.