 Deep vein thrombosis (DVT) is defined as development of thrombosis within the deep veins of the pelvis or lower limbs.
 Thrombus formation is a dynamic, multifactorial process that depends on a fine balance of physical and biochemical factors. The causes of thrombosis include three main causes: vessel wall injury, hypercoagulability, and venous stasis which is known as Virchow's triad.
 Early detection of deep venous thrombosis is very important not only to initiate anticoagulant therapy, but also very important to prevent further complications and to reduce morbidity and mortality.
 Diagnosis of DVT depends on clinical examination, laboratory and radiological investigations.
 Development of DVT is affected by many factors either genetic or acquired risk factors like age, Trauma, Cancer, Surgery, Pregnancy, Obesity, Immobility, hospitalization, hormonal therapy, inherited and acquired hypercoagulable states, anaesthesia, myocardial infarction, history of DVT, varicose veins, infections, inflammatory bowel disease, dehydration, and renal impairment are common risk factors.
 Compression ultrasonography is the first-line imaging tool for diagnosis of DVT because it is safe, easily accessible, cost-effective, and reliable.It is accurate to determine the size, chronicity, and degree of occlusion ofthrombus which is very helpful for making the decision of starting medical management or interventional techniques.