Background: Quasi-moyamoya disease (quasi-MMD) is a rare cerebrovascular disease and its clinical features and natural history remain unclear. The aim of the study is to describe the clinical characteristics and the natural histories of this disease, with analysis of the risk factors for future cerebrovascular events. Methods: We identified 64 patients with quasi-MMD from 693 moyamoya vasculopathy patients referred to our hospital between 2011 and 2015. Demographic data, associated disorders, clinical manifestation, angiographic findings, natural history, and risk factors for cerebrovascular events were analyzed. Results: Patients included in the study had a mean age of 31.5 years. A unimodal age distribution was noted. Atherosclerosis was the most frequently associated disorder. Forty-five (70.3%) patients had ischemic events as their initial clinical manifestation and 14 (21.9%) patients presented as hemorrhagic stroke. The majority of patients presented with Suzuki grades 3 and 4 (20.3% and 42.2%). The annual risk of cerebrovascular events was 19.4% per patient-year. Prior hemorrhage (HR 2.77, 95% CI 1.20-6.41) and ischemic stroke (HR 2.77, 95% CI 1.26-6.07) were 2 risk factors for future events. Conclusions: Several clinical characteristic differences were observed in our mainland China cohort compared with the Japanese and European cohorts. The annual risk of cerebrovascular events was relatively high in quasi-MMD patients. Patients with prior hemorrhage and ischemic stroke were inclined to have future cerebrovascular events. Close follow-up is needed for these patients.