The aim of the study was to examine the role of regulatory T-cells CD4+CD25+Foxp3+ (Treg) in the development of autoimmune disorders at multiple sclerosis and determination of the relationship of quantitative and functional deficiency of these cells with clinical picture of the disease. Immunophenotype of peripheral blood of 52 patients with multiple sclerosis was investigated by flowcytometry. The study demonstrated reduction in the number and functional activity of Treg in peripheral blood of multiple sclerosis patients at the acute stage and increase of their content in remission. Dependence of the duration of the autoimmune process and severity of multiple sclerosis on the number of Treg was marked. It was shown the important role of Treg in the maintenance of immunological tolerance at multiple sclerosis.