Deep vein thrombosis Deep vein thrombosis (DVT) is a blood clot in a major vein, usually in the legs and/or pelvis. Thrombosis occurs when the blood changes from a liquid to a solid state thereby producing a clot. If the blood clot occurs within a major vein, the condition is known as deep vein thrombosis (DVT). The most common veins affected by DVT are those of the legs or within the pelvis (lower abdomen). Deep vein thrombosis is a common but difficult to detect illness that can be fatal if not treated effectively. Deep vein thrombosis is a major complication in patients who have had orthopedic surgery or pelvic, abdominal, or thoracic surgery
