Free perforation of the bowel due to cancer in Crohn's disease is very rare. One case found among 75 cases of Crohn's disease is reported. The perforation occurred in a mucinous adenocarcinoma of the ascending colon in a 54-year-old woman with a 17-year history of Crohn's disease, who had undergone two previous operations of small bowel and colonic resection. A right hemicolectomy was performed; the patient had an uneventful recovery and does not show recurrence of cancer at 31-month follow-up. This is in contrast with a recent review, in which a very poor prognosis was claimed for the perforated colonic cancer in Crohn's disease.