Objective To explore the causes of deep vein thrombosis in lower extremities (DVT). Meth-ods Retrospective analysis of 411 patients with DVT being treated in our hospital from 2004 to 2009. Results 301 (73.2%) cases were with definite causes and 110( 26.8%) cases without definite causes. 195 cases occurred follow-ing operations and 68 cases following wounds and fractures. 122 cases accompanied with medical conditions ,50 cases occurred following pregnancy or child birth,39 cases suffered from cancer, 19 cases suffered from infection of lower extremity or local lesion,67 cases had past history of DVT. Conclusions Suggest that surgery, wound and fractures, postpartum, cancer, chronic illness inducing long-term bed stay and past history of DVT might correlate with DVT.