OBJECTIVE: To evaluate the outcomes of bypass surgery for adult moyamoya and compare different surgical modalities by performing a comprehensive meta-analysis of relevant studies. METHODS: A systematic literature search was performed and articles regarding different treatments for adult patients with moyamoya were included. Odds ratios (ORs) were calculated to evaluate stroke recurrence, mortality, perioperative complications, and angiographic revascularization among different surgical methods and conservative treatment (CT). RESULTS: A total of 17 studies with 2224 adult patients with moyamoya were included in the meta-analysis. Compared with CT, surgical revascularization significantly decreased the future stroke events in the total population ([OR] 0.404; 95% confidence interval [CI] 0.279-0.585; P < 0.001) and in the hemorrhagic-onset patients as well (OR 0.259; 95% CI 0.138-0.486; P < 0.001). However, for those patients with moyamoya and ischemia, there was no significant difference for future stroke events between the bypass and CT groups (OR 0.470; 95% CI 0.140-1.579; P = 0.222). Bypass also showed no mortality reduction compared with CT (OR 0.372; 95% CI 0.120-1.154; P = 0.087). For different surgical techniques, no differences for future stroke events, mortality, and perioperative complications were found between direct bypass and indirect bypass, whereas the degree of angiographic revascularization was better in the direct bypass group than in the indirect group (OR 4.720; 95% CI 1.222-18.230; P = 0.024). CONCLUSIONS: The bypass treatment was superior to conservative treatment in preventing recurrent stroke in adult patients with moyamoya, especially in those with a hemorrhagic onset. Direct bypass is associated with better revascularization results compared with indirect bypass.