The association between cancer and thrombosis is well established. Venous thromboembolism (VTE) is considered a main cause of mortality and morbidity in cancer patients and is commonly underestimated by oncologists. In recent years the incidence rates of VTE have notably increased. Several studies have clearly shown that cancer patients who are diagnosed with VTE present a poorer prognosis. The Spanish Society of Medical Oncology (SEOM) presents the guidelines for thrombosis and cancer in order to improve the prevention and management of VTE.