Five patients (four female, one male) with multiple sclerosis were managed at the Hospital for Sick Children, London, between January 1978 and June 1983. The age at which first symptoms occurred varied from three to 14 years. Focal seizures occurred in three cases and an encephalopathic process in three cases, and there was evidence of progressive intellectual deterioration in all five children. Computed tomography showed low-density lesions in the white matter of all five. Electroencephalograms were abnormal in all cases, and in two the disturbance was severe. Oligoclonal bands were present in the cerebrospinal fluid of two children. Four of the five children had abnormal responses to pattern-reversal stimulus.