Deep venous thrombosis with subsequent pulmonary embolism remains a significant cause of morbidity and mortality in hospitalized patients. Although prophylactic treatment may reduce the incidence of deep venous thrombosis by up to 70 percent, it is estimated that only 32 percent of hospitalized patients at high risk receive adequate prophylaxis. Older patients, obese patients and patients undergoing orthopedic procedures of the lower limbs are at particularly high risk of developing deep venous thrombosis. Both mechanical and pharmacologic measures provide effective prophylaxis. Newer treatment protocols have greatly reduced the incidence of drug side effects, particularly bleeding.