9056 Background: Thalidomide (T) is effective for treating MM but is associated with an increased incidence of VTE, especially when combined with other agents. Consequently, prophylaxis in patients receiving T-containing regimens has been recommended. However, the true risk of VTE is uncertain and the effectiveness of prophylaxis has not been established. We performed a systematic review to determine the incidence of VTE and the effect of prophylaxis in MM patients receiving T-containing regimens. Methods: MEDLINE and EMBASE were searched from 1966 to 11/16/2006. Only randomized controlled trials (RCT) and prospective cohort studies (PC) were included. Studies evaluating post-transplant maintenance therapy were excluded. Both authors independently screened and reviewed identified publications, and extracted data of pre-specified variables. Incidence estimates were calculated as proportions along with 95% CI. Results: 363 papers were identified but only 80 were relevant and reviewed. 45 studies (6 RCT and 39 PC) involving 1,886 patients receiving T-containing regimens met inclusion criteria. 9 studies clearly stated objective testing was used to confirm a diagnosis of VTE. The incidence of VTE is summarized in the table . We found 12 trials that used prophylaxis. None included appropriate control groups to allow assessment of effectiveness. Based on limited data, the incidences of VTE with prophylaxis were: ASA 13.9% (95% CI 9.1–19.9%), fixed low- dose warfarin 21.9% (95% CI 16.9–27.5%), therapeutic-dose warfarin 0% (95% CI 0–5.5%), and low molecular weight heparin 13.3% (95% CI 10.5- 16.6%). Conclusions: The incidence of VTE in MM patients receiving T-containing regimens ranges from 3% to 22%, depending on the patient type and agents used. Given the lack of level I/II evidence, recommendation for routine prophylaxis for patients receiving T- containing regimens is premature. A safe and effective antithrombotic regimen has yet to be identified. [Table: see text] No significant financial relationships to disclose.