The present article analyzes the parameters of plasma hemostasis in patients with a post-operative complication (venous thrombosis). The statistically significant results have been received that are indicative of the risk of postoperative venous thrombosis of the lower extremities after surgery on their main vessels. These data point to the persistence of elevated risk in patients with thrombotic events. The post-operative complications in the form of hemostatic disorders most frequently occurred in elderly patients. It is argued that the study of the hemostatic system is the most acceptable method for the early diagnostics of venous thrombosis during postoperative examination of the patients with occlusion of the large vessels following surgery. The triggering factors for the development of postoperative venous thrombosis are the damaged vessel wall, changes in the functional state of the hemostatic system and the slowed down blood flow.