Patients with multiple myeloma are at relatively high baseline risk of developing thromboembolic events (TEE), usually deep vein thromboses. There are numerous contributing factors, among them certain treatment regimens that include thalidomide or related compounds such as lenalidomide combined with glucocorticoids and/or cytotoxic chemotherapy. The risk of developing TEE appears to be particularly high when these immunomodulatory agents are combined with anthracyclines as treatment of newly-diagnosed disease. Up-front combinations including thalidomide plus pulse dexamethasone and/or alkylating agents are associated with an intermediate risk, whereas the same regimens for relapsed/refractory myeloma seem to be associated with the lowest risk. Several different thromboprophylaxis strategies have been effective in lowering the risk of developing clots: daily aspirin (81-325 mg/day), full-intensity warfarin (INR 2-3), and prophylactic enoxaparin (40 mg SQ daily). Low, fixed-dose warfarin may also reduce the risk of TEE, but the data on this are disputable. None of these TEE prevention strategies have been prospectively compared head-to-head, so the choice often reflects physician and/or patient preferences. The available evidence upon which one might make such a decision is reviewed here.Individuals with multiple myeloma (MM) are at increased risk for developing thromboembolic events (TEE) compared to the general population. 1 The exact incidence is difficult to determine since reported TEE rates likely vary according to the level of diagnostic vigilance. For example, in one retrospective chart review at the Cleveland Clinic, which has an established imaging algorithm for evaluating patients with MM and monoclonal gammopathy of uncertain significance who have symptoms of a possible TEE, the reported rate was approximately 10%.1 In contrast, the rates documented in patients treated with melphalan-prednisone or dexamethasone as part of large multicenter studies without uniform algorithms for documenting TEE were 5% and 3%, respectively.2,3 It is likely the actual background incidence falls in the 5-10% range. Factors that have been suggested as contributory to the risk of TEE in people with MM include newly diagnosed disease status 4 ; immobility due to pain and/or surgery; indwelling central venous catheters; extrinsic venous compression by plasmacytomas; acquired abnormalities in platelet function, 5 clotting factors, 6 and the coagulation cascade 7-9 ; the presence of inherited factors such as Factor V Leiden; and treatment with immunomodulatory agents including thalidomide and lenalidomide. The risk of developing TEE during therapy with combination regimens containing thalidomide and lenalidomide will be discussed, followed by recommendations on prevention and treatment.