This study aimed to identify predictive factors for cerebral infarction after bypass surgery in adult patients with moyamoya disease (MMD) using quantitative parameters in 4D-CT perfusion software.A total of 108 patients who underwent combined revascularization, including superficial temporal artery-middle cerebral artery (STA-MCA) anastomosis and encephalo-duro-myo-synangiosis (EDMS), in our hospital between September 2019 and August 2023 were analyzed retrospectively. Preoperative relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), relative mean transit time (rMTT), and relative time to maximum residual function (rTmax) perfusion parameters were obtained using 4D-CT perfusion software. These quantitative parameters, combined with related clinical and angiographic factors, were statistically analyzed using univariate and multivariate regression analyses to determine the significant predictors of cerebral infarction after bypass surgery.Acute cerebral infarction occurred in 12 patients postoperatively. Univariate analysis showed that a history of previous ischemic events (P = 0.024), higher Suzuki stage (P = 0.006), higher modified Rankin score (mRS) (P = 0.013), rCBV (P = 0.026), rMTT (P = 0.001), and rTmax (P < 0.001) were associated with postoperative cerebral infarction. Further multivariate regression analysis showed that a history of previous ischemic events (OR = 12.830, 95%CI = 1.854-875.672, P = 0.031) and higher rTmax (OR = 16.968, 95%CI = 2.035-141.451, P = 0.009) were independently associated with new postoperative cerebral infarction. The cutoff value for rTmax was 2.025 (AUC = 0.935).Previous ischemic event history and rTmax greater than 2.025 are independent risk factors for predicting cerebral infarction after combined revascularization with high sensitivity in adult patients with MMD. These patients should be more cautious when deciding on combined revascularization.© 2024. The Author(s).