324 patients operated on the organs of abdominal cavity small pelvis and retroperitoneal space were examined by the method of I-125-fibrinogen accumulation and contrast phlebography. In 109 (33.6%) patients thrombosis of deep veins of lower extremities was diagnosed, among which in 24 cases (7.5%) it was proximal. In most cases thrombosis was predisposed by postthrombotic disease and chronic venous insufficiency of lower extremities, circulatory disturbances of the 2-3 degree, tumors, obesity, preoperative thrombophilia. Combination of 2 and more risk factors increased possibility of intravascular thrombosis. The rate of clinically registered pulmonary artery embolism (14,833 general surgical patients were avau label) made up 1.2%; in 54 (0.3%) of operated patients it was the cause of death. Postoperative lethality of embolism made up 13%. Four risk levels of development of thrombo-embolic complications were established: low (common rate of thrombosis--10.3%, proximal--1.4%, clinically evidenced pulmonary artery embolism--0.7%, with lethal outcome--0.02%), medium (28.5; 6.5; 2; 0.76%, respectively), high (80.4; 17.8; 6; 2.8%, respectively) and very high (93.3; 26.6; approximately 8; approximately 4, respectively). The prevalence of thrombo-embolic complications in patients urge surgeons and reanimatologists to carrying out prophylactic to reduce the risk of intravascular thrombosis in pre- and postoperative period.