We studied the frequency of venous thrombosis in children and adolescents with malignant neoplasms receiving treatment in a specialized hospital. For 14 years, there were 142 patients with new thrombotic complication. At the stages of treatment of the underlying disease the incidence of symptomatic venous thrombosis, confirmed by the data of an ultrasound diagnostic study, ranged from 0.76 to 7.43 % per year. A 0.43±0.07 % average annual growth rate in the number of cases of venous thrombosis diagnosis in this category of patients was established. A relatively low prevalence of floating agglutinative thrombus and pulmonary embolism has been noted. The share of catheter-associated thrombosis reached 53 % among all patients with thrombosis. Ultrasound support during CVC placement reduces the risk of catheter-associated thrombotic complications.