['Arteriovenous malformations (AVMs) can be treated successfully, but treatment can pose unacceptable risks if the AVM is located in eloquent cortex. Because AVMs are developmental lesions, the location of primary cortical function may be deranged. We used magnetic source imaging (MSI) to identify the central sulcus and to determine whether primary cortical function was shifted in a set of 30 patients. We correlated these findings with outcome after treatment.', 'We retrospectively analyzed the clinical data of 30 patients with AVMs who underwent MSI. Nonparametric statistical comparisons were made to correlate the proximity of AVMs to primary cortex and somatosensory shift to outcome at 12 months.', 'Using MSI, 14 patients (47%) were found to have AVMs involving primary cortex, and 10 patients (33%) were found to have shift in the somatosensory homunculus. Primary cortical involvement was neither required nor sufficient to cause shift (Mann-Whitney U test, z = -0.02, P = 0.31). Patients with AVMs involving primary cortex fared worse after treatment than did patients with AVMs that spared primary cortex (Mann-Whitney U test, z = -2.3, P = 0.02). The presence or absence of shift did not correlate with outcome after treatment (Mann-Whitney U test, z = -0.18, P = 0.48).'] Does magnetic source imaging demonstrate altered cortical distribution of function in patients with arteriovenous malformations?