Twenty-three pediatric patients with white matter abnormalities on MR images were evaluated retrospectively to assess the contribution of MR compared with CT in diagnosing these conditions. In addition, the MR findings in major categories of white matter diseases were analyzed for sensitivity in detecting the presence of an abnormality. White matter disease categories included demyelinating disease (five cases), dysmyelinating disease (eight cases), developmental white matter abnormalities (four cases), and white matter abnormalities of unknown origin (idiopathic) (six cases), as seen on long TR images. We found that MR is not more sensitive than CT in detecting disease in the demyelinating or dysmyelinating categories, although it is more sensitive than CT in detecting the degree of disease present. In cases of developmental delay, MR is distinctly more useful than CT in demonstrating abnormalities of myelination. And in the idiopathic group, MR detected the presence of focal white matter abnormalities on long TR images in children with neurologic complaints and normal CT. MR may serve to redefine and broaden the spectrum of reported imaging abnormalities in pediatric patients.