Inflammatory bowel disease (IBD) is associated with an increased risk for thromboembolic events. Aim of this study was to examine the relationship of hyperhomocysteinemia and thrombosis in IBD patients and to assess the role of this factor in addition to other known prothrombotic abnormalities. IBD patients with a history of thrombosis (n = 22) and sex-, age-, and diagnosis-matched IBD controls (n = 23) were studied. Homocysteine (tHcy) was assessed before and after methionine loading. Plasma levels of protein C, protein S, antithrombin III, and fibrinogen and the presence of anticardiolipin and antiphospholipid antibodies were determined and genetic testing for factor V Leiden and the prothrombin gene mutation was performed. Results showed that fasting homocysteine levels in IBD patients with a history of arterial or venous thrombosis tended to be higher than in IBD controls, although not significantly. The increase in homocysteine levels after methionine loading was significantly higher in IBD patients in the arterial thrombosis group than in IBD controls (40.9 +/- 17.7 vs. 27.2 +/- 9.9 microM; P < 0.05). Among the other prothrombotic factors, only factor V Leiden was significantly associated with a history of venous thrombosis (20 vs. 0%). At least one risk factor was found in 64% of the IBD patients with previous thromboembolic complications. We conclude that there is an association between hyperhomocysteinemia and a history of arterial thrombosis in IBD patients. We confirm the high prevalence of factor V Leiden in IBD patients with a history of venous thrombosis. In the majority of IBD patients with previous thromboembolic complications, at least one prothrombotic risk factor is detected.