Several studies have shown that there might be a relationship between previous history of appendectomy or cholecystectomy and the subsequent risk of colorectal cancer. In order to investigate these hypotheses, a case-control study was set up to compare the history of appendectomy and cholecystectomy as well as the presence of cholelithiasis in patients with colorectal carcinoma vs patients with gastric carcinoma. The study was performed in the 727 patients included in the Registry of Digestive Cancers of the Côte d'Or and treated at the Dijon University Hospital during the period 1981-1987. These patients were well matched to those of the whole registry population for sex, age, stage, and residence distributions. In females, in comparison to the gastric cancer patients, a personal history of appendectomy was more commonly observed in case of right colonic cancer (odds ratio: 3.5; P less than 0.01) and a personal history of cholecystectomy in case of left colonic cancer, in particular when considering only those earlier than 10 years (odds ratio: 3.2; P less than 0.05). In contrast, the risk of rectal cancer was lower in case of a cholecystectomy performed more than 10 years earlier (odds ratio: 0.2; NS) and in case of cholelithiasis (odds ratio: 0.4; P less than 0.05). In males, there was no difference between cases and controls as for the proportion of appendectomies, cholecystectomies or cholelithiasis. These observations are consistent with the hypothesis that the appendix as a lymphoid organ plays a protective role in colon carcinogenesis, in particular in women.(ABSTRACT TRUNCATED AT 250 WORDS)