We report on 14 cases of intestinal adenocarcinoma complicating Crohn's disease, seven occurring in the small bowel and seven in the large bowel. In both locations, two-thirds of patients were male. The average ages at the time of diagnosis of Crohn's disease and of cancer were similar between the two groups of patients: 28 and 48 years, respectively. The diagnosis of cancer was suspected or obtained preoperatively in only four cases of large bowel cancer; in two patients with large bowel cancer and five with small bowel cancer, the diagnosis was made at laparotomy. In the remaining cases, only careful histologic examination revealed the carcinoma. Six small bowel cancers were located in the ileum, and five colonic cancers were distal to the splenic flexure. Two small bowel and one large bowel cancer were multifocal and had surrounding mucosal dysplasia. All tumors, except one small bowel cancer, underwent resection. Survival correlated with stage of tumor at resection; no patient with regional or distant metastasis survived five years, in comparison with an 83 percent five-year actuarial survival rate of patients with tumor confined to the intestinal wall. Mean survival was six months for patients with small bowel cancer in comparison with 65 months for patients with large bowel cancer, reflecting a tendency toward more advanced lesions in the small bowel cancer group.