In a retrospective case control review we determined the cholecystectomy frequency of 479 index cases of colonic carcinoma and 479 age, sex, and admission date matched controls. The frequency distribution patterns of cholecystectomy with reference to subsite specific cancer of the large bowel were determined. The cholecystectomy frequency in patients with proximal colonic cancer was higher than those in whom cancer was present in areas other than the proximal colon (12.3 per cent vs. 6.6 per cent, P less than 0.02). There was a gradient of previous cholecystectomy history from the proximal colon to the rectum. The overall frequency of previous cholecystectomy in the index cases was 8.1 per cent while that in the matched control was 5.4 per cent. The difference was not statistically significant. However, the cholecystectomy frequency of the proximal colonic cancer subgroup was significantly higher than its matched control group (12.3 per cent vs. 4.6 per cent, P less than 0.02). The difference was greater in females with proximal colonic cancer compared with their matched controls (14.3 per cent vs. 3.6 per cent, P less than 0.02). Our data supported the hypothesis that either (1) altered bile salt metabolism after cholecystectomy may increase colonic cancer formation, or (2) gallbladder disease and colonic cancer may share common etiologic factors.