BACKGROUND Clinical research on moyamoya disease (MMD) has focused on symptomatic outcome such as transient ischemic attacks. Neurocognitive function in children critically affects social outcome and is closely related to quality of life. This study is the first to analyze the neurocognitive profiles of children with MMD before and after surgery. METHODS Sixty-five patients were selected out of 137 who underwent surgery for MMD between 2006 and 2008. The preoperative and postoperative neurocognitive function was tested using the Korean version of the Wechsler Intelligence Scale for Children-Revised (KEDI-WISC-R) and the Bender Gestalt Test (BGT). Pre- and postoperative profiles of patients with or without major infarctions were compared. Patients with borderzone infarctions were analyzed as well. RESULTS Preoperatively, patients had age-appropriate full-scale intelligence quotient (FSIQ) and verbal IQ (VIQ) scores, which were maintained after surgery. There was significant improvement in performance IQ (PIQ) (p = 0.01) and BGT scores postoperatively (p < 0.01). Among the subtests, Coding showed significant improvement postoperatively (p < 0.01). Preoperatively, patients with major infarctions had significantly lower FSIQ (p < 0.01), VIQ (p = 0.01) and PIQ (p < 0.01) scores compared with those without infarctions. The pre- and postoperative neurocognitive profiles of the patients with borderzone infarctions fell between those of patients with absolutely no infarctions and those of patients with major infarctions. CONCLUSIONS Considering the natural history of MMD, which leads to a drastic decline in neurocognitive functions, the present findings indicate a role for early active surgery to save the intellectual abilities of children with MMD.