Venous thrombosis is a medical condition where a blood clot, known as a thrombus, forms in a vein. This often occurs in the deep veins of the legs, a condition referred to as deep vein thrombosis (DVT). Factors that can increase the risk of venous thrombosis include prolonged immobility, certain medical conditions, and some medications. If a thrombus breaks loose, it can travel to the lungs, causing a serious condition called pulmonary embolism. Symptoms of venous thrombosis may include swelling, pain, and redness in the affected area. Early diagnosis and treatment are essential to prevent complications.