Aim. To study the role of little-known factors in development, course and treatment of acute ileofemoral venous thrombosis (IFVT) of lower extremities. Material and methods. Comprehensive diagnosis and treatment of 432 patients with acute ileofemoral venous thrombosis were analyzed. There were 289 (66.9%) women and 143 (33.1%) men aged 19-84 years (mean age 51±2.2). The diagnosis was confirmed by clinical manifestations and sonography data. Hemostatic system state was assessed using the level of activated partial thromboplastin time (aPTT), prothrombin time (PTT), prothrombin index (PTI), international normalized ratio (INR), thrombin time, fibrinogen, platelet count and kaolin clotting time. Results. It was found that the highest incidence of diseases was noted during fasting of Ramadan holy month and the summer season (June-August). These data confirm the role of hot climate in development of disease, that is caused by excessive sweating and dehydration followed by hemostatic disorders. Occlusive form of IFVT was detected in 345 (79.9%) patients, parietal and floating thrombosis was found in 51 (11.8%) and 36 (8.3%) cases respectively. Ultrasonic imaging devoted to thrombus structure and venous system state was significant to determine optimal management and monitoring of therapy’s effectiveness. The same method revealed iliac veins stenoses in 47 patients during recanalization. Current complex conservative therapy with anticoagulants, antiplatelet agents and elastic compression has achieved positive results in 86.1% of patients. Conclusion. It was observed the regularity of IFVT occurrence during hot period of the year and Ramadan month, as well as trigger factors. So seasonal preventive treatment may be recommended.