The purpose of the study: to study the amount of irizin in the blood serum of children with Type 1 diabetes considering the duration of clinical course and determine the role of irizin in diagnosing the diabetic myopathy. The study included 90 children with Type 1 diabetes (T1D) (average age 13,7±0,4 years old). Depending on the duration of the disease, 3 groups were formed: 1 group — 26 children under 1 year with T1D; group 2 — 27 children — duration of T1D from 1–5 years; group 3 — 37 children with T1D duration more than 5 years. The control group included of 25 conditionally healthy children of a representative age and gender. All children were evaluated for their muscle and fat mass and their indices, ultrasound examination of skeletal muscles, and determination of irisin levels in the blood serum by ELISA. It was established that with increasing durations of T1D there was a redistribution of the component body composition in the form of a decrease in the specific the muscle mass and an increase in the percentage of fat mass, as well as changes in the ultrasound pattern of skeletal muscles characterized by a decrease in the thickness of the muscle fibers, a infraction of the normal architecture of muscle and increased echogenicity of muscle bundles. It was established that in the first years of the disease, the decrease in muscle mass was accompanied by a decrease in the level of irisin, whereas with the prolonged course of T1D there was an increase in it, which was accompanied by loss of muscle mass and infraction of the architecture of skeletal muscles. Thus, increasing the level of irisin can be used as an additional marker for the development of diabetic myopathy.