Objectives: The risk for thrombotic events is increased in inflammatory bowel disease. The factors responsible for such a risk are poorly defined. Recently, an elevated homocysteine level is emerging as a risk factor for thrombosis. The aim of this study was to determine the levels of homocysteine in a well-characterized population of patients with Crohn's disease and to compare it to controls. Methods: The levels of homocysteine were determined in 105 well-characterized patients with Crohn's disease and 106 controls. The levels of folate and B12, which are involved in the metabolism of homocysteine were determined as well. Patients were treated with steroid preparations only. Results: Homocysteine levels were significantly elevated in the patient population. Elevated levels were correlated with both low B12 and folate levels, but folate deficiency turned out to be a more important factor. Low B12 levels were in correlation with the involvement of the terminal ileum. No correlation was found between homocysteine levels and either disease activity or involvement of the terminal ileum. Conclusions: Homocysteine levels are increased in patients with Crohn's disease and this finding is inversely correlated with folate levels. Supplementation of folate to patients with Crohn's disease may be warranted. (C) 2000 by Am. Coll. of Gastroenterology.