Thrombosis of unusual sites (hepatic vein thrombosis, splenic vein thrombosis, mesenteric vein thrombosis, ovarian vein thrombosis, retinal vein thrombosis, cerebral vein thrombosis, portal vein thrombosis, axillary and subclavian vein thrombosis) are life-threatening disorders that often goes unrecognized. Most often thrombosis ofatypical locations develops in patients with inherited hemostasis defects - genetic thrombophilia. Thrombosis of unusual sites often accompany acquired abnormalities of hemostasis, which include antiphospholipid syndrome, hypercoagulability associated with pregnancy, oral contraceptives use, malignant tumors, in conditions of ovarianhyperstimulation in IVF programs. In case of thrombosis of unusual sites screening for hereditary forms of thrombophilia and antiphospholipid syndrome should be performed and timely administration of anticoagulant therapy is critical. Analysis of genetic and acquired abnormalities of hemostasis allows you to select a group of patients requiring longterm anticoagulation therapy and mandatory anticoagulant prophylaxis in situations with a high risk of thromboembolic complications (pregnancy, surgery).