Collagenous colitis is a rare clinical and pathological entity characterized by watery diarrhea and deposition of collagen beneath the surface epithelium of the colon. Its etiology is unknown. We present a careful retrospective clinicopathological analysis of six patients with collagenous colitis diagnosed at our hospital during a three-year period. Three of the patients had had a Yersinia enterocolitica infection, detected by stool culture and elevated serum antibody titers, preceding the diagnosis of collagenous colitis. Four patients had duodenal villous atrophy, which in two patients was refractory to a gluten-free diet. We propose that Yersinia enterocolitica infection may be a triggering factor for the development of collagenous colitis in some cases. Duodenal villous atrophy not responding to gluten withdrawal is common in association with collagenous colitis.