This study investigated the effect of Gamma Knife radiosurgery for the treatment of arteriovenous malformations (AVMs) on neuropsychological functioning. We examined neuropsychological performance in 10 patients before and after radiosurgical treatment with the Leksell cobalt-60 Gamma Knife unit. The patients included 7 right-handed women and 3 right-handed men. Three patients had left hemisphere AVMs, 4 had right hemisphere AVMs, and 3 had midline AVMs. Each patient was given neuropsychological testing within 1 week before Gamma Knife radiosurgery. Testing was repeated an average of 11.4 months after treatment. There were no statistically significant differences between pre- and postradiosurgical neuropsychological test scores on any measure. Pretreatment AVM diameter as measured on magnetic resonance scans ranged from 1.6 to 6.5 cm. After treatment, 2 AVMs disappeared, 4 decreased slightly in size, and 4 remained unchanged. We conclude that Gamma Knife radiotherapy in this sample of patients was neither detrimental nor beneficial to neuropsychological functioning.