Until recently venous and arterial thrombosis were considered mechanistically distinct entities. However, their separate nature has been challenged by several studies showing that these conditions share a number of risk factors such as age, obesity, infections and the metabolic syndrome. The existence of an association is further supported by the finding that patients with venous thromboembolism are at higher risk of arterial events and vice versa. This review article addresses the association between venous and arterial thrombosis and its clinical and therapeutic implications. We conclude that arterial and venous thrombosis are mechanistically different, but that common risk factors are more relevant and frequent than previously thought.