Summary. Introduction. Multiple sclerosis (MS) usually presents in young adults and is uncommon in children, especially when less than 10 years of age. Diagnosis is difficult in this age group, and we consider that Poser’s diagnostic criteria should be used. Clinical case. A five year old girl presented with multiple symptoms and signs including headache, vomiting and a pyramidal syndrome. Initially there was spontaneous improvement. However, subsequently progressive worsening of the pyramidal syndrome occurred with marked cerebellar and general deterioration. On cerebral MR there were areas of increased resonance in the medulla, cerebellum, pons, periventricular white substance and basal ganglia. Acute disseminated encephalomyelitis was diagnosed (ADEM) and treatment started with corticosteroids. There was a satisfactory response and complete recovery after a few days. Eight months later she presented with right optic neuritis (ON). There was alteration of visual and somatosensory evoked potentials, signs of diffuse cerebral damage on the EEG, oligoclonal bands (OB) of IgG in the cerebrospinal fluid and new areas of increased resonance on MR. A third episode occurred 22 months after the first, with cerebellar symptoms and more areas of demyelination on MR. Conclusions. As a consequence of the low incidence of MS in the first ten years of life, the characteristic features at this age are less well defined than in adults. With reference to this case, we review the differential diagnosis with ADEM since it may be very difficult or impossible to distinguish these conditions in the early stages of the illness