BACKGROUND: The object of this study was to compare the long-term outcomes in adult patients with moyamoya disease (MMD) with posterior circulation involvement (PCi) treated through surgical revascularization with those in adult patients without PCi. METHODS: The records of 32 consecutive adult patients with ischemic-type MMD who were treated with revascularization were reviewed. Twelve of these patients (38 %) had PCi at initial onset. Clinical characteristics of the patients with PCi were compared to those without PCi. Neurological outcomes were assessed using the modified Rankin Scale (mRS) in the preoperative and postoperative follow-up periods. A five-year Kaplan-Meier stroke risk was calculated. RESULTS: The frequency of presenting with infarction was significantly higher among patients with PCi than among those without PCi (p = 0.006). mRS scores in the preoperative period were significantly higher in patients with PCi than in patients without PCi (p = 0.0004). There were no significant differences in mRS scores between the preoperative and postoperative follow-up period in patients with PCi (p = 0.3), nor were there any between the preoperative and postoperative follow-up periods in patients without PCi (p = 0.2). The five-year Kaplan-Meier risk of surgical morbidity and ipsilateral stroke was 14.3 % in surgically treated hemispheres with PCi versus 14.9 % in surgically treated hemispheres without PCi (p = 0.96). CONCLUSIONS: PCi at initial onset was significantly correlated with poor outcome. Revascularization for the middle cerebral artery territory in patients with PCi was effective at preventing recurrent ischemic stroke.