Nineteen patients admitted to The Mount Sinai Hospital with Crohn's disease between 1960 and 1989 had 20 adenocarcinomas of the small intestine. Sixteen patients had regional enteritis and three, ileocolitis. There were 15 males and four females. Carcinomas occurred in association with fistulas (four patients), fistulous tracts (three patients), excluded bowel (five patients/six cancers) and multiple strictures (three patients). None of the patients in our study had cancer develop in the first decade of Crohn's disease, and 11 had carcinoma in the third decade. As cancers occurred in three patients with multiple strictures admitted for strictureplasty, we recommend that all strictures be widely opened and carefully examined prior to strictureplasty, with frozen section biopsies of all suspicious areas. The possibility of small intestinal Crohn's carcinoma should be suspected in patients with long-standing disease, with or without excluded bowel, who present with sudden change in symptoms, especially after a lengthy quiescent period. Cancer should also be considered in patients in whom complete obstruction fails to resolve with adequate decompression and in those with multiple strictures.