We wanted to determine the neurocognitive profile of adult patients with moyamoya disease prior to neurosurgical intervention. The experience of three United States medical centers, Columbia University, University of Illinois at Chicago, and the University of Texas Southwestern Medical Center at Dallas, were combined. Clinical data from adult patients (N = 29) referred for neuropsychological evaluation from 1996 to 2008 were reviewed. Neurocognitive functioning was assessed using standardized neuropsychological tests and all data were converted to z-scores. Memory, attention, processing speed, verbal memory, visuo-spatial, language, and executive functions were examined. Cognitive dysfunction was defined as performance in two or more cognitive domains 1.5 standard deviations below age-corrected normative means OR one or more cognitive domains two standard deviations below age-corrected normative means. Manual strength and dexterity, as well as depressive symptoms, were also assessed. Two-thirds of patients demonstrated neurocognitive dysfunction. A large proportion of patients were found to have pronounced cognitive dysfunction (>2 SD below the mean) on tests of processing speed (29%), verbal memory (31%), verbal fluency (26%) and executive function (25%). Manual strength and dexterity were also affected in many patients, with impairment found in 36-58% of patients. Twenty-eight percent of patients reported moderate to severe depression, but depressive symptoms did not correlate with neurocognitive findings. A large proportion of adults with moyamoya disease demonstrate disruption of neurocognition in a broad range of functions, particularly those mediated by subcortical and frontal regions. The pattern of deficits suggests a mechanism of diffuse small vessel disease possibly caused by chronic hypoperfusion.