In recent years hyperhomocysteinemia has been established as a new risk factor for arterial and venous thrombosis. Since patients with inflammatory bowel disease (IBD) frequently suffer from thromboembolic events, we studied the prevalence and clinical significance of hyperhomocysteinemia in Greek patients with ulcerative colitis (UC) and Crohn's disease (CD). In 108 consecutive fasting IBD patients (53 UC and 55 CD) and 74 healthy controls (HC), a standard record of various clinical thrombotic risk factors was completed by interview, and fasting serum concentrations of total homocysteine (tHcy), folate, cobalamin, creatinine, cholesterol, HDL, LDL, and triglycerides were measured. The concentration (mean +/- SD) of serum tHcy was significantly higher in UC (15.9 +/- 10.3 micromol/liter) and CD patients (13.6 +/- 6.5) than in controls (9.6 +/- 3.4, P < 0.05). Both UC and CD patients had lower levels of folate than HC (P < 0.05). Covariance analysis of age, gender, and all clinical variables indicated that the differences in homocysteine levels between IBD patients and HC remain significant even after adjustment for these covariates. In conclusion, mild hyperhomocysteinemia is common in Greek IBD patients and may account for the increased thrombotic risk of these patients.