This study investigated whether human intestinal microvascular endothelial cells undergo endothelial-to-mesenchymal transition and contribute to fibrosis in human and experimental inflammatory bowel disease (IBD). Results found that chronic inflammation induces transdifferentiation of intestinal mucosal microvascular cells into mesenchymal cells, suggesting that the intestinal microvasculature contributes to IBD-associated fibrosis through the novel process of endothelial-to-mesenchymal transition.