Cancer and critical illness are predisposing factors for the development of catheter-related deep vein thrombosis. This chapter discusses specific catheter-related factors that increase the risk of thrombosis, as well as strategies for prophylaxis against the development of these vascular complications. Treatment options will also be covered, including management of the catheter and options for pharmacologic therapy. Finally, consideration will be given to concomitant thrombocytopenia, a frequent comorbid condition in patients with malignancy.