We report two cases of multiple sclerosis with concentric patterns of demyelinated foci on MR images. These were compared with the pathological data of Balò's disease. The T2-weighted MR images displayed alternating high and low signal areas which probably corresponded to the concentric type of demyelination. Our two cases were characterized by their acute onset and their regression following corticosteroid therapy. This suggests that Balò's disease may be a transient disease and not always associated with a fatal course.