Deep vein thrombosis (DVT) and pulmonary embolism (PE) are major sources of morbidity and mortality. In young individuals the incidence of DVT is of 1/100,000 people; at middle age it is approximately 1/1000, which is also the overall incidence; thereafter, it increases steeply and in old age approaches 1%/year. DVT is a multifactorial disease involving a variety of risk factors, many of which are common. It is nowadays accepted that the interaction of multiple risk factors over time determines the risk of thrombosis.