The prevalence of gallstone disease in 145 consecutive patients with colorectal cancer was compared with gallstone prevalence in 4,159 subjects randomly selected from a population. The group of patients had a significantly higher prevalence of gallstone disease than the population (odds ratio = 1.59; 95 percent confidence limits 1.04-2.45), whereas cholecystectomies occurred with equal frequency in the two groups. There was a nonsignificant trend toward more right-sided cancers in patients with gallstones than in patients without. These results, together with available literature, give substantial evidence for an association between gallstones and colorectal cancer, an association which is not due to cholecystectomy being a predisposing factor to colorectal cancer. Sporadic findings of an association between cholecystectomy and colorectal cancer can be explained by the above relationship.