BACKGROUND AND PURPOSE: Methods have not been well developed and tested to predict the extent of remote degeneration in the central nervous system that follows cerebral infarction. We hypothesized that the extent of infarction overlap with the cerebral hemispheric course of the corticospinal tract (CST) on structural MR imaging predicts the extent of ipsilateral cerebral peduncular atrophy in patients with chronic stroke. MATERIALS AND METHODS: Hemiparetic patients (n = 34) with supratentorial unilateral infarctions who were at least 1 year poststroke onset and enrolled in research protocols of Constraint-Induced Movement therapy underwent volumetric T1 MR imaging of the brain. The following measures were calculated for each patient: 1) the maximal proportion of the CST in the cerebral hemisphere on axial section that was overlapped by infarction, 2) total infarction volume, and 3) the ratio of the cross-sectional area of the ipsilateral cerebral peduncle to the area of the contralateral cerebral peduncle (peduncular asymmetry ratio). Correlation analyses evaluated the predictive value of CST injury or infarction volume for the peduncular asymmetry ratio. RESULTS: CST injury correlated significantly with the peduncular asymmetry ratio (r = -0.65; P < .001), whereas infarction volume did not (r = -0.31; P = .09). CONCLUSIONS: The extent of postinfarction CST injury in the cerebral hemisphere predicts the extent of ipsilateral cerebral peduncular atrophy. More generally, the findings suggest that the extent of remote wallerian degeneration of a fiber tract is strongly related to its extent of injury directly at the site of infarction.