[Collagenous colitis: a disease difficult to define].

The Authors report a case with watery chronic diarrhoea not related to malabsorption or to inflammatory bowel disease or to intestinal neoplasm. Colonic biopsy, performed during colonoscopy, with the histologic finding of collagenous material in the subepithelial space associated to epithelial alterations and to the presence of inflammatory cells, confirmed the diagnosis of this rare pathologic condition. The pathogenesis of the syndrome, however, is still unknown.