The purpose of this study is to investigate developmental neuroplasticity in children who sustained unilateral perinatal brain injury. Studies have begun to examine the functional organization of the brain following early injury and have found patterns of activity that differ from typically developing children. Examination of the structure of the brain has also revealed alterations in the intact tissue, specifically in the white matter. These abnormalities are evident as low white matter volumes in discrete regions within the injured and uninjured hemispheres. Together, these findings suggest that the pattern of connectivity and coherence of axonal tracts within the white matter in both hemispheres may be atypical. The goal of the current study is to determine whether white matter tracts are altered following an injury that occurs early in development. In the present study, a magnetic resonance imaging technique called diffusion tensor imaging (DTI) was used to investigate the presence and structural integrity of white matter fiber tracts in children who sustained unilateral perinatal brain injury, typically from stroke. A DTI-based index of white matter tract integrity, anisotropy, was measured in predefined regions within specific white matter tracts. Additionally, a measure of white matter tract cross-sectional size was also obtained. These indices were measured in 16- to 23-year-old individuals who sustained perinatal brain injury (n = 6) and age matched controls (n = 30). White matter tracts that were likely to have projected to, or received projections from the site of injury were analyzed for possible direct effects of the lesion. On a more exploratory basis, other major white matter tracts within both hemispheres were examined to determine whether there are more extensive effects of the early localized disruption. The study found reduced anisotropy and smaller cross sectional size in white matter tracts that were directly impinged upon by the lesion. Additionally, more distal white matter tracts in both the injured and uninjured hemisphere also had reduced anisotropy compared with controls. Alteration of white matter structure in both hemispheres indicates that the effect of a unilateral perinatal lesion is not confined to the local development of that brain region. Rather, a unilateral lesion is associated with secondary changes in white matter more remote from the site of the lesion in both hemispheres.