Objective: The contribution of cortical reorganization to motor recovery after a subcortical stroke is uncertain. The purpose of the study was to investigate the relationship between changes in motor cortex organization, and the degree of motor function after a subcortical stroke.Methods: Transcranial magnetic stimulation mapping of the corticomotor projection to the hand was performed in 27 patients who had suffered a subcortical ischemic stroke resulting in an upper limb motor deficit up to 23 years previously. Corticospinal conduction was assessed by measurements of motor evoked potential latency, amplitude and threshold. Motor function in the upper limb was assessed using the Motor Assessment Scale for Stroke and measurements of grip strength.Results: Motor maps for the hand were displaced on the affected side relative to the unaffected side in 17 patients. In 10 of these patients in whom corticospinal conduction had normalized, there was a strong positive correlation between the magnitude of the map shift and grip strength in the affected hand (r = 0.79; P = 0.006). In the other seven patients with a map shift, in whom corticospinal conduction was still impaired, there was a tendency for a larger map area to be associated with better motor function, and in the group as a whole there was a correlation between map area and grip strength (r = 0.52; P = 0.005).Conclusions: The present findings provide evidence that the cortical plasticity and reorganization that occurs after a subcortical stroke is functionally significant and contributes to motor outcome. (C) 2004 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.