Deep vein thrombosis (DVT) occurs when a blood clot (thrombus) forms in one or more of the deep veins in the body, usually in the lower legs, thighs, pelvis and sometimes in the arms. Deep vein thrombosis can cause pain or swelling, but also can occur with no symptoms.Deep vein thrombosis can develop with certain medical conditions that affect how the blood clots. It can also happen if you don'...