MRI examination of 41 patients with clinical definite multiple sclerosis showed white matter lesions of high proton T2 signal consistent with demyelination in 76% and CSF abnormalities present in 76%. Of patients with CSF abnormalities, 26% had normal MRI scans; conversely 26% of patients with MRI abnormalities had negative CSF studies. Thus a significant number of multiple sclerosis patients had negative results on either MRI or CSF examination, while only 5% had normal results on both tests.