&NA;The relationship between gastrointestinal neoplasms and Crohn's disease is poorly defined. The purpose of this study was to characterize the features of gastrointestinal malignancies that developed in Crohn's patients. In this retrospective review the authors identified six patients with Crohn's disease who developed such lesions over a 20‐year period: four patients had colorectal cancers and two had ileal malignant neoplasms. Patients averaged 52.7 years of age (range, 21 to 61 years). Three patients were men and three women. Five of the six patients had endured Crohn's disease for more than 20 years. Only two lesions were diagnosed before surgery. The colorectal lesions were predominantly right‐sided and all occurred in bowel segments with active Crohn's disease. The lesions demonstrated aggressive histologic features: three of six tumors were poorly differentiated, one of the five adenocarcinomas was mucinous, and three of the colorectal cancers were Dukes' B or C lesions. Four of six patients survived five or more years. There was a single malignant carcinoid, which represents the seventh case report of a carcinoid tumor occurring in a patient with Crohn's disease. This study indicates that patients with Crohn's disease develop a wide variety of small bowel and colorectal cancers. Furthermore, it suggests that Crohn's patients with colonic disease should periodically undergo surveillance colonoscopy.