OBJECTIVE: Whether surgery should be performed in patients with acute onset of moyamoya disease (MMD) is controversial. This study aimed to determine optimum operative time for patients with MMD. METHODS: We retrospectively analyzed 57 patients with MMD admitted between January 2016 and AMC 2017. All patients consented to combined revascularization. Considering the time interval between acute onset of MMD and surgery, we divided all patients into an early group and later group (>90 days between MMD onset and surgery). We compared postoperative complications, neurologic improvement, and favorable outcome between groups to estimate optimum operative time of revascularization. RESULTS: More patients in the early group presented with ischemic events compared with the later group (18/28 vs. 11/29, P = 0.047). The difference in worst preoperative mRS score (>= 3) between groups was not statistically significant (3/28 vs, 3/29, P = 0.96/). Rate of postoperative complications in the early group was significantly higher than in the later group (39.2% vs. 13.7%, P = 0.029). There was neurologic improvement in 50.0% of patients in the early group and 75.9% of patients in the later group (P = 0,043), The rate of favorable outcome after revascularization in the later group (89.7%) was higher than in the early group (78.6%), but there was no significant difference (P = 0.251). CONCLUSIONS: It seems more reasonable to opt for delayed revascularization for patients with acute-onset MMD but the decision must take into account the morbidity of ongoing ischemic or hemorrhagic events.