Grading white matter lesions on CT and MRI: a simple scale. We developed and tested a simple three-point scale for grading white matter lesions in anterior and posterior regions of the brain. Twenty four CT scans and 24 MRI scans were separately judged by 11 and five observers, respectively, on the presence and severity of white matter lesions. The observers were radiologists and neurologists. For CT scans, these periventricular changes were graded according to their extent as absent, or partly involving the white matter, or extending up to the subcortical region. The MRI lesions were graded as no lesion or only a single one, multiple focal lesions, and multiple confluent lesions. The pairwise agreements of all possible combinations of observers for each scan were corrected for chance (kappa statistics; maximal agreement 1.0). The weighted kappa value, for anterior and posterior regions combined, was 0.63 for CT scans, and 0.78 for MRI scans. This three-point scale for two separate regions seems suitable as a basis for cross-sectional or longitudinal studies of large series of patients. 