Two hundred and twenty-three patients with colorectal carcinoma were treated consecutively at the University Hospital of South Manchester from May 1976 to January 1981. Twenty-four patients (10.7 per cent) were found to have more than one colorectal carcinoma. In 18 patients this was recognized either immediately or within 6 months of the initial diagnosis--synchronous carcinoma. In the other six cases a second carcinoma was found at a later time--metachronous carcinoma. The incidence of synchronous, and consequently the combined incidence of synchronous and metachronous carcinoma, was higher than previously documented. The anatomical distribution of the multiple carcinomas and the sex incidence in these patients was similar to that seen in patients with a single carcinoma of the large bowel. A high association of adenomatous polypi with multiple large bowel carcinomas was observed. The possibility of more extensive colonic resection in the younger patient with a favourable carcinoma is discussed.