Mesenteric vein thrombosis (MVT) is uncommon condition. The purpose of this study was to assess prevalence of prothrombotic disorders in these patients. Eleven patients with MVT were screened for protein C, protein S, and antithrombin III deficiencies. Gene analysis was performed by polymerase chain reaction. A prothrombotic disorder was detected in 9 (81.8%) patients. Factor V Leiden, methylenetetrahydrofolate reductase TT677, and prothrombin G20210A mutations were found in 2 (18.2%), 2 (18.2%), and 5 patients (45.4%), respectively. Protein S, protein C, and antithrombin III deficiencies were present in 1, 1, and 2 patients, respectively. Four patients (36.3%) had combined defects. Thus, prothrombotic disorders may have a causative role in the pathogenesis of MVT, and these patients must be screened for these disorders.