The purpose of this study was to use diffusion tensor imaging (DTI) with fiber tractography (FT) to demonstrate focal lesions of the corticospinal tract (CST) in hemiparetic patients with cerebral palsy (CP) who showed no specific focal lesions on conventional brain MRI. Four hemiparetic patients with CP (three left hemiparesis, mean age: 2.5 years, range: 0.9-7.0) and four age-matched controls were recruited. DTI was performed using a 1.5-T system with a synergy-L Sensitivity Encoding head coil. Fractional anisotropy (FA) and apparent diffusion coefficients (ADC) were measured using the region of interest (ROI) method. We estimated the asymmetric anisotropy index (AA) and asymmetric mean diffusivity index (AD) to evaluate the asymmetry between right and left CSTs. All four patients showed interrupted FT at the affected periventricular white matter (PVWM) level compared to that of the opposite side; this was not detected on conventional brain MRI and explained the hemiparesis of these patients. Compared to the data of controls, all patients showed significant AA and AD only at the PVWM level. DTI with FT demonstrated focal lesions at the PVWM level. We conclude that DTI with FT may be a useful modality for investigating focal lesions in hemiparetic patients with CP.