We report the preliminary results of an ongoing study of multiple sclerosis (MS) in childhood. The investigations include an analysis of the clinical picture and course. Multiple sclerosis in early childhood may present atypically, with a symptomatology suggesting diffuse encephalomyelitis, meningeal reaction, brain oedema, seizures, impaired consciousness and in some cases take a lethal course. Imaging studies including MRI and MR-spectroscopy, CSF-analysis, electrophysiology (VEP, BAEP, SER), and virological and immunological investigations are performed. So far 15 children have been studied. Their age at the onset of the disease ranged from 3 to 15 years. Abnormal CSF-findings with pleocytosis and oligoclonal IgG bands were present in 11 and 10 out of 15 patients respectively. MRI revealed numerous white matter lesions in the brain stem and cerebral hemispheres. VEP, BAEP and SER's were abnormal in most children. Proton magnetic resonance spectra from plaques exhibited a 50-80% decrease in N-acetyl aspartate, which is a potential marker of vital neuronal tissue, a decrease of the creatine pool and an increase of choline-containing compounds. Lactate was not increased. Our observations of MS in early childhood cast doubt on some of the previous notions concerning a latency period of several years between the exposure to a still unknown agent and the manifestation of MS. In view of atypical features in the initial phase, it would seem desirable to record cases of encephalomyelitis of undetermined origin as potential cases of MS and to register the further course for verification or exclusion.