SummaryWe have reported a series of 351 patients undergoing resection for diverticulitis, in 27 of whom a coexisting carcinoma in the same segment was found, an incidence of 7.7 per cent. In 13 instances cancer was not suspected preoperatively. Even by palpation of the isolated protected segment of involved bowel, we were unable to diagnose accurately the presence of the carcinoma, an error of 40.7 per cent. We believe that until more exacting methods of diagnosis are made available, and in view of the increase in life expectancy, as well as the increased incidence of cancer, where there is the slightest measure of doubt, the apparent diverticular segment should be removed as if it were frank cancer. We further plead for higher levels of suspicion and earlier surgical extirpation.