Objective of the study was to compare blood clotting parameters in lymphoma patients with or without venous thrombosis (VT), as well as to analyze the duration and outcome of anticoagulant therapy in children, adolescents and young adults with lymphoma, whose program treatment was complicated by VT.Materials and methods . The analysis included 28 patients with lymphoma (Hodgkin lymphoma – 5, non-Hodgkin lymphoma – 23), aged from 2 to 25 years (median – 16.0 years), whose program treatment in 2005–2017 was complicated by VT. The case-control study was carried out to compare the parameters of blood coagulation. The control group consisted of 22 patients, aged from 2 to 20 years (median – 15.5 years) with the same diagnosis, age, therapy protocol and phase of treatment who had no thrombotic complications. The comparison group consisted of 35 healthy children aged from 3 to 18 years (median – 14.0 years).Results . There was no difference in majority of blood clotting parameters in lymphoma patients with or without VT. Hyperfibrinogenemia and an increased D-dimers level distinguished patients with lymphoma, regardless of the presence or absence of thrombosis, from healthy children of the same age (р<0.05). Anticoagulant therapy up to 3 months received 10 patients, for 4–6 months – 4, for 7–12 months – 12, up to 18 months – 2. One adult patient with a homozygous mutation 20210G>A gene of the factor II takes warfarin continuously for a long time after relapse of VT. Complete recanalization of the thrombosed vessel occurred within the first 3 months in 9 patients, within 4–6 months – in 1, within 7–12 months ‒ in 4. Partial recanalization within 3–12 months was confirmed in 8 patients. Vein obliteration, mainly the internal jugular vein, as the outcome of VT occurred in 6 patients within 4–12 months.Conclusion . Detection of routine blood clotting parameters does not allow identifying patients with thrombosis among children, adolescents and young adults with lymphoma. Fibrinogen and D-dimers levels were significantly higher in lymphoma patients, than in healthy children. Anticoagulant therapy for 3–12 months led to the complete or partial recanalization of VT in 79 % of patients. To detect blood clotting parameters by thrombosis development, as well as to reveal and monitor transient and permanent risk factors are necessary to specify the cause of VT and to determine the appropriate anticoagulant therapy.