A case is reported of collagenous gastrobulbitis on collagenous colitis in a 57-year-old woman with a 6-month history of watery diarrhea. Low serum levels of total proteins and albumin and increased fecal elimination of alpha1-antitrypsin were the only abnormal laboratory test results. Biopsy specimens from the colon, rectum, antrum, fundus, and duodenal bulb showed a thick subepithelial band composed of ultrastructurally normal collagen immunohistochemically negative for collagen IV and laminin. The diarrhea resolved with prednisone and responded to this treatment after a relapse 6 months later. One year later the patient developed severe alimentary intolerance and secondary weight loss. This symptom also responded to the same treatment. However, the collagen deposition did not disappear in the second biopsy samples of colonic and gastric mucosa. Only six cases have been previously reported with gastric and/or duodenal subepithelial collagenous deposition. Four were associated with collagenous colitis. One of these presented a subepithelial collagenous band in the terminal ileum. All these features suggest that this collagen deposition may affect the entire digestive tract with variable intensity, extension, and symptoms.