Objective: Transient neurological events (TNEs) are frequently observed after revascularization surgery for moyamoya disease (MMD). However, clinical features and pathophysiology of TNEs in MMD are still unclear. This study was aimed to clarify the incidence and time course of TNEs and to determine the independent predictors of TNEs in MMD. Patients and methods: A total of 195 hemispheres in 171 consecutive patients with MMD who had undergone combined direct and indirect bypass surgery were analyzed. Preoperative clinical characteristics and radiographic features were recorded. The incidence and clinical feature of postoperative TNEs were evaluated. Multivariate logistic regression analyses were performed to identify the risk factors for postoperative TNEs. Outcomes were compared between patients who had TNEs with those without TNEs at the time of discharge. Results: Postoperative TNEs were detected in 40 (20.5%) of 195 operated hemispheres, including 17 (42.5%) aphasia, 9 numbness of the extremities (22.5%), 6 seizures (15%), 5 motor weakness (12.5%), 4 dysarthria (10%) and 6 others (15%). The incidence of TNEs was significantly higher in adult patients than in pediatric ones. Multivariate analysis revealed that female, left-sided surgery and the presence of the edematous lesion was an independent predictor of TNEs after surgery in MMD (OR, 3.0; 95% CI, 1.1–8.2; P = 0.03, OR, 2.9; 95% CI, 1.2–7.0; P = 0.02 and OR, 17.4; 95% CI, 5.7–53.0; P < 0.01, respectively). DSA stage (OR 0.05, 95% CI 0.0–0.5, p = 0.005; OR 0.08, 95% CI 0.0–0.4, p = 0.008), PCA involvement (OR 2.75, 95% CI 1.0–7.4, p = 0.046), left-sided surgery (OR 2.73, 95% CI 1.2–6.5, p = 0.022) and edematous lesion (OR 21.2, 95% CI 7.6–59.7, <0.001) were significantly associated with TNE severity. Compared with patients without postoperative TNEs, no significant differences in mRS score between the two groups were detected. Conclusions: Female, left-sided surgery and edematous lesion were independent risk factors for postoperative TNEs; the left-sided surgery and edematous lesion were also independently associated with the severity of TNE. Although patients with postoperative TNEs had worse neurological status during the perioperative period, postoperative TNEs had no associations with worse mRS score at the time of discharge. © 2019