In order to investigate the relation between the occurrence of colorectal cancer and food consumption in Hokkaido, Japan, etiological factors of colorectal cancer were investigated through an ecologic study using official food consumption and mortality statistics concerning colorectal cancer, and through a community-based case-control study. The ratio of 'animal foods' to 'plant foods' and that of 'animal protein' to 'plant protein' had a significant correlation with the mortality rate in colorectal cancer. The percentage of fat energy was much more contributory than the absolute amount of fat. Traditional Japanese foods tended to prevent while Western foods tended to promote colorectal cancer. Odds ratios for Japanese foods were low for colon cancer, and those for Western foods were high for rectum cancer. Relative amounts of foods are more contributory than their absolute amounts. An increase of colorectal cancer in Japanese people may be attributable to the increase in the relative amounts of Western foods. Reduction of the ratio of animal foods to plant foods (i.e., a reduction in relative amounts of Western foods or an increase in relative amounts of Japanese foods) may lend to the prevention of colorectal cancer.