Article abstract—We obtained two conventional unenhanced T2-weighted brain MRI scans, separated by an interval of 24 to 36 months, in 281 patients with multiple sclerosis (MS). At the time of each scan, clinical disability was rated using the Kurtzke Expanded Disability Status Scale (EDSS). Changes in disability between the two examinations correlated weakly but significantly with the number of new (Spearman9s rank correlation coefficient = 0.13; p = 0.02) and enlarging (Spearman9s rank correlation coefficient = 0.18; p = 0.002) MRI lesions. This result suggests that brain T2--weighted MRI is a useful supplementary marker of disease activity in definitive (phase 111) clinical treatment trials in MS.