OBJECTIVE: Constraint-induced movement therapy (CIMT) has been shown to improve upper extremity voluntary movement and change cortical movement representation after stroke. Direct comparison of the differential degree of cortical reorganization according to chronicity in stroke subjects receiving CIMT has not been performed and was the purpose of this study. We hypothesized that a higher degree of cortical reorganization would occur in the early (less than 9 months post-stroke) compared to the late group (more than 12 months post-stroke). METHODS: 17 early and 9 late subjects were enrolled. Each subject was evaluated using transcranial magnetic stimulation (TMS) and the Wolf Motor Function Test (WMFT) and received CIMT for 2 weeks. RESULTS: The early group showed greater improvement in WMFT compared with the late group. TMS motor maps showed persistent enlargement in both groups but the late group trended toward more enlargement. The map shifted posteriorly in the late stroke group. The main limitation was the small number of TMS measures that could be acquired due to high motor thresholds, particularly in the late group. CONCLUSION: CIMT appears to lead to greater improvement in motor function in the early phase after stroke. Greater cortical reorganization in map size and position occurred in the late group in comparison. SIGNIFICANCE: The contrast between larger functional gains in the early group vs larger map changes in the late group may indicate that mechanisms of recovery change over the several months following stroke or that map changes are a time-dependent epiphenomenon.