Since the mid-nineties, it is clear that the cause of the white matter abnormalities cannot be found in at least half of the affected children. This finding has led to a more systematic analysis of the unclassified white matter disorders and the identification of "new" disorders. A group of patients can be assumed to share one and the same disorder when the patients share important clinical, biochemical, pathological and/or MRI characteristics. In our search for homogeneous groups of patients with a white matter disorder, sharing important characteristics, MRI has played an important role.