Venous thromboembolism (VTE) is a common event in cancer patients and one of the major causes of cancer-associated mortality and a leading cause of morbidity. In recent years, the incidence rates of VTE have notably increased; however, VTE is still commonly underestimated by oncologists. VTE is considered an adverse prognostic factor in cancer patients in all settings. In 2011 the Spanish Society of Medical Oncology (SEOM) first published a clinical guideline of prophylaxis and treatment of VTE in cancer patients. In an effort to incorporate evidence obtained since the original publication, SEOM presents an update of the guideline for thrombosis and cancer in order to improve the prevention and management of VTE.