The authors report a case of reorganization of the cortical control of movement caused by radiation necrosis based on an analysis of functional magnetic resonance (fMR) imaging data acquired during a finger-tapping paradigm. Radiation necrosis in this patient extended from the parietal lobe anteriorly to the primary motor cortex (PMC), and fMR imaging demonstrated an increase in activation in the ipsilateral supplementary motor area. This is similar to the consequences of invasion by glial tumors into the PMC.