Clinical observation on the association of gallstones and colorectal cancer. A possible association between gallstones, colorectal cancer, and gastric cancer was investigated. The age distribution and mean age of the two cancer groups were identical. The incidence of gallstones in 378 colorectal cancer cases and 869 gastric cancer cases was 7.1% and 5.5%, respectively. Of colorectal cancer cases, 33 cases with multiple carcinomas had a significantly higher gallstone incidence than cases with a solitary carcinoma--24.2% and 5.5%, respectively. The mean age was 5 years older in gallstone cases than in those without gallstones in both cancer groups, and it was 4 years older in multiple-carcinoma cases than in solitary-carcinoma cases in the colorectal cancer group. These results suggest that the higher levels of same causative factors (i.e., dietary fat) are associated with a longer duration of gallstone formation and colorectal cancer development as demonstrated by multiple colorectal-carcinoma cases. 