The aim of this work was to study the levels of 25 (OH) vitamin D (calcidiol - CD) and 1.25 (OH)2 vitamin D (calcitriol - CT) in the blood of patients with hemorrhagic fever with renal syndrome (HFRS) depending on the severity, the period of the disease, and elucidation of the role of vitamin D metabolism disorders in the pathogenesis of HFRS. Patients and methods. 114 patients with HFRS, aged 18–55 years (average age 37.4 ± 2.6 years) were under the supervision. Among them 53 patients were with moderately severe form, 61 - with severe one. The determination of serum calcidiol and calcitriol levels was carried out by high performance liquid chromatography.  Determination of the level of cytokines (INF-γ, TNF-α, IL-2) was carried out by the enzyme immunoassay using reagents of Vector-Best CJSC (Novosibirsk). Results. The lowest concentration of calcitriol and calcidiol in the blood serum is observed in the oliguric phase with moderately severe and severe forms of HFRS. The more severe the disease, the more evident the deficiency of vitamin D active metabolites is. The study of cytokines in these patients revealed a sharp increase in TNF-α, a monotonously low level of IFN -γ, and a decrease in IL-2 in the febrile and oliguric phases. A reliable direct correlation between calcitriol and IL-2, as well as between calcitriol and INF-γ, and a significant inverse correlation between the concentration of calcitriol and the level of TNF-α were revealed. Conclusions. Deficiency of vitamin D active metabolites may be one of the mechanisms contributing to the appearance of hypocalcemia affected hypocalceuria in the midst of HFRS. The presence of correlations of calcitriol with IL-2, INF-γ, and TNF-α indicates a possible role of deficiency of the vitamin D active metabolite in the development of immunological disorders in HFRS.