Superficial temporal artery-middle cerebral artery anastomosis is generally considered as an effective method in improving damage associated with intracerebral occlusions in moyamoya disease. Hemodynamic changes caused by revascularization are the cause of many postoperative complications. Of the 186 consecutive surgeries for moyamoya disease at our hospital from 2015, we herein presented one case of adult-onset moyamoya disease that manifested symptomatic local cerebral edema and local hypoperfusion caused by the 'watershed shift'. A 67-year-old woman presented with limb numbness on the right side and underwent superficial temporal artery-middle cerebral artery anastomosis, resulting in neurological dysfunction and the formation of a reversible high-signal lesion at left frontotemporal lobes on T2-weighted images along with a decrease in perfusion values on 123I N-isopropyl-p-iodoamphetamine single-photon emission computed tomography, while the anastomotic vessel was patent on magnetic resonance angiography. This phenomenon of hypoperfusion area (left frontotemporal lobe) remote to anastomotic site (left temporal lobe area) led to the diagnosis of the 'watershed shift' phenomenon. In light of the hypoperfusion induced by 'watershed shift', the patient was treated with fluid replacement. With the gradual recovery of perfusion, the patient presented significantly improvement both on the magnetic resonance imaging findings and neurological symptoms. In conclusion, regional cerebral edema with hypoperfusion, possibly due to cerebral ischemia and the 'watershed shift' phenomenon, may be another novel entity that needs to be considered as a potential complication after extracranial-intracranial bypass for moyamoya disease.