OBJECTIVE: The epidemiology of asymptomatic moyamoya disease (MMD) is still unclear, and the best management remains controversial. The aim of this study is to evaluate the prognosis of these patients with different management, conservative follow-up, or surgical treatment. METHODS: This prospective cohort study screened a series of 696 consecutive MMD patients from 2009-2015. Patients with any episodes of hemorrhage and ischemic stroke or TIA were excluded. Finally, 61 patients who were followed up for at least 12 months were included, with 52 patients who underwent surgical treatment and 9 patients who underwent conservative follow-up. Patients were divided into 2 groups: surgical and conservative. Advert events including newly hemorrhage and ischemic stroke and death were compared between the groups. Relationships between disease progression and collaterals and cerebral blood flow were analyzed separately. RESULTS: The mean follow-up period was 56.32 months (range, 11.3-112.62 months). During the follow-up period, 3 patients had symptomatic progression in the conservative group, 1 suffered a hemorrhage, and 2 had TIAs. Among the patients in the surgical group, 6 of them experienced TIAs. Kaplan-Meier analysis showed that patients receiving surgeries had a longer symptom-free time compared with patients in the conservative group (P = 0.015). Decreased cerebral blood flow had no influence on disease progression in patients in both groups. Existence of extracranial to intracranial collaterals showed a better outcome for patients in the surgical group but not the conservative group. CONCLUSIONS: Surgical treatment may be a better choice for patients with asymptomatic MMD. And patients with better collateral circulations, especially extracranial to intracranial collateral arteries, may have a better prognosis.