Ten patients with Crohn’s disease of the upper gastrointestinal tract were studied. All patients had either gastric or duodenal involvement, or both, and all had typical Crohn’s disease elsewhere. In one patient, an esophageal lesion of Crohn’s type was present. Upper abdominal pain and nausea and vomiting were the predominant clinical symptoms; signs of gastric outlet obstruction signalled the onset of gastroduodenal involvement. In four patients not previously known to have Crohn’s disease, gastric outlet obstruction was the initial sign of the disease, but all four proved to have concurrent disease of the ileum or colon. The histologic changes in the upper gastrointestinal lesions were similar to those in the ileum and included transmural chronic inflammation, granulomas, and marked submucosal fibrosis. Other disease processes known to produce similar changes were carefully excluded.