We reviewed the magnetic resonance imaging scans from 22 serial studies of 5 patients with Balò's concentric sclerosis collected during the past 3 years. The data showed the concentric lesions did not occur simultaneously but developed step by step in a centrifugal direction. The development of lesions was preceded by an enhancing ring relatively devoid of demyelination and was followed by progressive demyelination occurring mainly at the inner aspect of the enhancement. The same process recurred on the edge of the previous enhanced zone. Thus, an appearance of concentric rings with alternating demyelinated and relatively myelin-preserved bands was formed.