Objectives: This retrospective study aimed to explore the impact of seasonal variations on the first ischemic events in patients with moyamoya disease (MMD). Patients and Methods: Based on the first-time ischemic event occurrence, 113 patients, including 84 with cerebral infarction and 29 with transient ischemic attack, who were diagnosed with ischemic MMD were divided into four groups: spring (March-May), summer (June-August), autumn (September-November) and winter (December-February). The incidence of cerebral infarction was considered as the primary parameter. The impact of seasonal variations on the occurrence of cerebral infarction was analyzed by Poisson regression model and seasonal analysis. Results: When summer was set as the reference, patients in summer were more significantly susceptible to develop cerebral infarction as compared with spring (IRR, 0.529, 95%CI, 0.299-0.937, p = 0.03), autumn (IRR, 0.441, 95%CI, 0.240-0.810, p < 0.01) and winter (0.500, 95%CI, 0.279-0.895, p = 0.02). The seasonality of the time series in summer (1.231) was substantially higher than that in the other three seasons (- 0.269 in spring, -0.656 in autumn and -0.306 in winter). No discrepancy in either NIHSS or mRS scores at admission was observed among the four seasons. Conclusion: Patients with MMD may be more vulnerable to cerebral infarction in summer compared with the other three seasons, and seasonal onset of cerebral infarction does not seem to be associated with the severity of neurological disability at admission.