Early onset multiple sclerosis (MS) has some peculiarities in the disease course. 56 patients with definite MS with the onset at the age under 15 years were included in this clinical, immunogenetical and neurophisiological study. The analyses of the relations between different clinical characteristics of MS in children has shown, that patients with onset under 10 years, had rare relapses, but more progressive development of disability in contrast to the patients with MS onset at the age of 11-15 years. Duration of the first remission was associated with the time to sustained disability in children with MS. The number and volume of MRI T2-positive lesions in the white matter of the brain was associated with the age of onset, duration of the disease and with the number of relapses. In several cases the phenomena of clinical-MRI dissociation was observed. Generic HLA-DRB1 genomic typing was performed in all the patients. High frequency of DR2(15) genotype in MS-affected children in comparison with the group of healthy controls was more expressed as compared with MS-affected adults. The comparison of frequencies of DRB1 alleles in transmitted, i.e. appeared in the affected child haplotypes and in non-transmitted haplotypes confirmed results of the case-control study showing the very significant association of MS with DR2 alleles and extremely significant--with its DR15 subtype in children. The data of transmission/disequilibrium test (TDT) analysis provide strong evidence for linkage of DR15 alleles and susceptibility to sporadic MS in patients with disease onset before 15 years. The positive experience of management (beta-interferon-1a) was shown in MS-affected children in three cases.