This study aimed to investigate the extent of microstructural changes in the major white matter fibers and to evaluate whether diffusion tensor imaging (DTI) adds any lateralizing information in children with medically intractable neocortical epilepsy secondary to focal cortical dysplasia. Patient group included twenty-three consecutively enrolled patients with medically intractable focal neocortical epilepsy and focal cortical dysplasia histopathologically confirmed. Thirteen patients (56.5%) had no visible lesion on the conventional magnetic resonance imaging (MRI). Fractional anisotropy (FA) was measured for regions of interest (ROIs) in each major white matter fiber. FA in patients was compared with eighteen age-matched healthy controls. Patient group had lower FA values at corpus callosum, bilateral inferior frontooccipital fasciculus (IFO), bilateral inferior longitudinal fasciculus (ILF) and left superior longitudinal fasciculus (SLF) compared to controls (p<0.05). In the left-side surgery group, the left SLF FA value was lower than controls, while in the right-side surgery group, the right SLF FA values were lower than controls (p<0.05). In the patient group as a whole, ipsilateral SLF FA was significantly lower than the contralateral SLF (p<0.05). Widespread decrease in FA values in the patients compared with the controls suggests that the pathologic changes extend diffusely to most major white matter tracts. In the patient group, the ipsilateral SLF to the seizure focus had greater change compared to the contralateral SLF. These data suggest that the detection of DTI abnormality has an added value to lateralization. © 2012 Elsevier B.V.