[WITH SPECIAL PLATE BETWEEN PAGES 466 AND 467] Brit. med. J., 1968, 2, 466-468 In a recent survey of Crohn's disease undertaken at the Radcliffe Infirmary three cases were encountered in which both carcinoma of the colon and Crohn's disease were present. As it is generally held that there is no association between these two diseases it seems important to report these cases and to discuss the possibility that a genuine association exists. Investigations.-Haemoglobin 7.2 g./100 ml. Blood filmmarked iron-deficiency changes. Stools-repeatedly positive for occult blood, negative for pathogens, no acid-fast bacilli on culture. Barium enema showed an irregular filling defect of the caecum, together with narrowing of a short segment of the pelvic colon.At operation in November 1949 the appearances were those of a malignant lesion of the caecum, to which the sigmoid colon and coils of terminal ileum were adherent. A right hemicolectomy, ileal resection, and sigmoid resection was carried out, with end-toend anastomosis of the left colon, and end-to-side ileotransverse colostomy.The caecum contained a large soft carcinoma which had partially infiltrated the caecal wall. There were adhesions between caecum and overlying loops of ileum. Histologically the tumour was a moderately differentiated papillary adenocarcinoma. Microscopically, some adhesions were inflammatory in nature and others were neoplastic. A mixed inflammatory infiltrate within the caecum extended well beyond the limits of the tumour, and within this infiltrate were granulomatous foci containing giant cells. There were marked submucosal fibrous thickening and fibrous infiltration of pericolic fat, and fissures were present. Within the ileum there was again pronounced subserosal and submucosal fibrous thickening, and the submucosa contained patchy mixed inflammatory infiltrate, including moderate numbers of giant cells. Enlarged mesenteric lymph nodes showed marked reactive hyperplasia but no evidence of malignancy. In summary the changes were typical of Crohn's disease involving the caecum and ileum.After the operation the patient developed a faecal fistula from the sigmoid resection site, but this eventually closed and she was discharged home three months after admission. She was readmitted four months later because the fistula had recurred. This was excised and the defect in the colon closed. She remained well for seven years.She was admitted again in 1957 and an intraperitoneal abscess adjacent to the ileocolic anastomosis was drained. Numerous adhesions were divided at the time. She had persistent diarrhoea after this operation and was readmitted a few months later with a fistula-in-ano, a fissure-in-ano, and an ischiorectal abscess. These were dealt with surgically and she was discharged considerably improved.She was next admitted in November 1958 with a small-intestinal obstruction. Laparotomy revealed a mass at the site of the ileocolic