Magnetic resonance imaging (MRI) was performed on 36 children and two adults (with clinical presentation during childhood) with white-matter disease of the central nervous system. Abnormalities were readily demonstrated in patients with multiple sclerosis, acute disseminated encephalomyelitis, leucodystrophies and subacute sclerosing panencephalitis: MRI demonstrated the extent and distribution of abnormalities more clearly than computed tomography for all these disorders. The abnormalities tended to be asymmetrical and multifocal in multiple sclerosis and acute disseminated encephalomyelitis, and more confluent and symmetrical in the leucodystrophies. Children with clinically isolated optic neuritis had a significantly lower frequency of MRI brain-lesions than adults with the same disorder. MRI should be regarded as the radiological investigation of choice when white-matter disease is suspected in children.