A 47-year-old female developed hyperperfusion syndrome after superficial temporal artery-middle cerebral artery (STA-MCA) bypass for moyamoya disease. She presented with right hemiparesis and motor aphasia due to left cerebral infarction. She underwent left STA-MCA bypass. One day after surgery, she manifested neurological deterioration. Magnetic resonance (MR) imaging 4 days after the operation indicated regional brain edema in the territory supplied by the bypass, and single photon emission computed tomography 17 days after the operation demonstrated hyperperfusion in that area. Symptoms improved within 1 week after surgery, and MR imaging showed disappearance of edema and return to the preoperative appearance. Such events are rare, but hyperperfusion syndrome may occur after STA-MCA bypass for moyamoya disease.