Deep vein thrombosis (DVT) occurs when blood clots form in the deep veins of the legs. The condition can be painful and may result in blood clots breaking free and traveling to the lungs (embolism), where they may obstruct blood flow and cause serious health problems or death.

DVT occurs most often among people over the age of 50. In recent years, researchers have identified a number of risk factors that may contribute to DVT. They include inherited conditions, long periods of immobility, pregnancy, recent surgery or trauma to the legs, smoking, cancer, use of birth control pills and certain forms of heart disease.

Once diagnosed, deep vein thrombosis is usually treated with medication that helps prevent additional blood clots from forming or existing blood clots from growing larger. Physicians may also prescribe special compression stockings that help blood flow upward through the veins of the leg. In serious cases, a device called a vena cava filter may be implanted into the veins of the leg. This basket–like device prevents blood clots from traveling up into the lungs.

Deep vein thrombosis is a type of thrombophlebitis. However, it should not be confused with a less dangerous form of thrombophlebitis called superficial vein thrombosis (SVT or phlebitis). SVT occurs when blood clots form in the surface veins of the legs. This condition is not as dangerous because these blood clots will not travel to the lungs.