Aim.The objective of the present study was to detect the most important predictors of the development of postoperative venous thromboembolic complications (VTE) in the high risk surgical patients undergoing the standard prophylactic treatment. Material and methods. The present prospective observational study included 140 patients with general surgical (47.9%) and neurosurgical (52.1%) pathology belonging to the high risk group. All  the patients underwent standard combined prophylactic treatment including elastic compression of the lower extremities and administration of direct anticoagulants within different periods after the surgical intervention. The compression ultrasonographic study of the venous system in the lower extremities was carried out during the first 12 hours after surgery and thereafter every 3—5 days. The patients in whom fresh thrombosis was detected were additionally examined with the use of perfusion scintigraphy of the lungs and/or echo-cardiography. All deceased patients were autopsied. Results. The overall occurrence of postoperative venous thrombosis was estimated at 27.9% (95% CI: 20.5—35.3), that of proximal thrombosis and pulmonary embolism at 8.6% (95% CI: 3.9—13.2) and 9.3% (95% CI: 4.5—14.1) respectively. The results of regression analysis indicate that the total number of individual risk factors (p<0.0001), paralysis of the lower extremities (p<0.0001), sepsis (p<0.0001), duration of stay in the intensive care unit (p=0.001), chronic heart insufficiency (p=0.001), masculine gender (p=0.003), bed rest regime in excess of 3 days (p=0.01), the history of  VTE (p=0.02), neurosurgical pathology (p=0.035), and catheterization of the central veins (p=0.042) are the most reliable predictors of the development of venous thrombosis. Stage by stage selection of risk factors has demonstrated that the most significant ones predicting the development of venous thrombosis were the total number of risk factors, the number of bed days spent in the intensive care unit, and masculine gender. The concomitant oncological process reduced the prognostic value of these factors. Further analysis revealed the strong positive correlation between the total number of risk factors and the probability of the development of postoperative venous thrombosis (r=0.982±0.134; p=0.018). The combination of three and more conditions predisposing to the development of venous thrombosis played the crucial role because it increased the probability of this pathology by a factor of 10 despite simultaneous standard prophylaxis.