IgG anti-endothelial cell antibodies (AECA) have been described in sera from patients with vasculitis and other immune disorders such as systemic lupus erythematosus. Presence of AECA may be relevant to the hypothesis that Crohn's disease (CD) is a form of intestinal vasculitis. The aim of this study was to search for IgG AECA among 141 patients with CD, 94 patients with ulcerative colitis (UC) and 71 healthy blood donors and to assess the relationship between AECA and demographic or disease data. The cut-off point was defined from the mean OD values + 2 SD obtained from healthy blood donors. Seventeen percent of sera from patients with CD were positive for IgG AECA, whereas 24.5% of sera from patients with UC were positive. Among disease data, only a significant relationship between presence of IgG AECA and CD activity was noticed. These results might reinforce the hypothesis that intestinal vascular injury may be an important event in CD. However, detection of AECA in an almost similar percentage of patients with UC is more suggestive of an immune response to hidden endothelial self-antigen exposed after endothelial cell damage or a further marker of disturbed immunoregulation in inflammatory bowel disease.