A vitamin status was studied in 32 children of both sexes at the age of 9-15 years with insulin-dependent diabetes mellitus within 2-3 years. The adequate consumption of all the vitamins studied was found only in two children. Polyhypovitaminosis was detected in 19% of these children. Deterioration of riboflavin metabolism observed was manifest, as a decrease in the vitamin content in tissues in line with an increase in its excretion with urine. As a result of this impairment metabolism of vitamins B6 and PP was disturbed with development of these vitamins secondary deficiency of the non-alimentary type. Obligatory correction of the water soluble vitamin deficiency in the patients with diabetes mellitus is discussed.