SummaryThe incidence of multiple primary adenocarcinomas of the colon at Charity Hospital in a 19‐year period was 2.1 per cent. The incidence of all multiple colonic and rectal malignancies was 4.1 per cent. Thirteen patients (0.5 per cent) had multiple metachronous adenocarcinomas, and 34 patients (1.6 per cent) had multiple synchronous adenocarcinomas.The possibility of a second carcinoma makes it imperative for the physician to obtain good diagnostic studies, bariumenema studies, and proctoscopy of every patient preoperatively. The resected specimen should be examined by the pathologist at the time of operation. Postoperatively, an annual physical examination, including proctoscopy and barium‐enema studies, is necessary.