The study analyzed the level of vitamin D(OH) in the blood serum in patients with depression aged 18-27 years, studied its relationship with clinical characteristics and features of the course of depression, suicidal behavior. There is a parallelism between the decrease in D(OH) level and the severity of depressive disorder. In assessing the risk of suicide, depending on the serum vitamin D(OH) concentration, it was found that a high risk of suicide in the group of patients with severe vitamin D deficiency was significantly more frequent than in the group of patients with normal vitamin D(OH) levels. When assessing the intensity of suicidal ideology, it was found that actual suicidal ideals with a specific plan and the intention to implement it were met only in the group with severe vitamin D deficiency. It was shown that a decrease in the vitamin D(OH) concentration in the blood is associated with a decrease in the cognitive abilities of patients. The determination of the level of vitamin D(OH) in serum can be used in assessing the severity of depressive states.