Thromboembolic events are common among patients with cancer as a consequence of cancer- and treatment-related factors. As these events are the second most frequent cause of death in this population, their prevention and treatment are important. Venous ultrasonography is the technique of choice for diagnosis, with sensitivity and specificity above 95 % in symptomatic thrombosis. Routine prophylaxis is not recommended for ambulatory patients, although it could be useful in selected cases. On the other hand, all inpatients should receive prophylactic therapy unless contraindicated. Therapy of thromboembolic disease is based on anticoagulants. Clinical trials demonstrate that the use of low-weight heparins is associated with a lower incidence of bleeding and recurrent thrombosis as compared with non-fractionated heparin or warfarin. Options for recurrent thrombosis include change to another anticoagulant agent, increasing doses of the same agent and cava filters.