Here we report a case of moyamoya disease in which cortical veins reddened after superficial temporal artery (STA) to middle cerebral artery (MCA) anastomosis, following postoperative hyperperfusion. A 37-year-old man with moyamoya disease suffered cerebral infarction in his right hemisphere. Single photon emission computed tomography (SPECT) showed impaired cerebral blood flow (CBF) in both cerebral hemispheres. The patient underwent STA-MCA anastomosis in the right cerebral hemisphere. During operation, soon after declamping the STA, cortical veins near the anastomosis site changed its color from blue to red. This change was repeatable by clamping and declamping of the STA. Postoperative SPECT and computed tomography (CT) demonstrated increased CBF and subarachnoid hemorrhage at the anastomosis site, suggesting the occurrence of postoperative hyperperfusion. By strictly controlling the patient's blood pressure, the syndrome resolved 1 week after the operation. We propose that the venous reddening after STA-MCA anastomosis may be a sign of postoperative hyperperfusion.