The incidence of large bowel cancer correlates internationally with the consumption of fat, protein or meat. Etiological hypotheses have been proposed, suggesting that a high-fat diet is related to an increased risk of large bowel cancer, while dietary fiber is claimed to have a modifying effect. However, while these hypotheses were derived from the analysis of the geographical distribution of colon cancer in humans, they are not unequivocally supported by the results of further epidemiological studies. This is particularly true for case-control studies which generally have not confirmed an association between diet and the risk of colorectal cancer at the individual level. Lack of uniformity among the findings of epidemiological studies concerned with the role of diet in the etiology of bowel cancer could be explained by 1. lack of sensitive and reproducible methods for assessment of diet in epidemiological studies, 2. lack of knowledge of the mode of action of dietary factors responsible either for the development of the tumor or for protection against it. Future epidemiological research on diet and large bowel cancer should deal with more precisely defined hypotheses in which the possible multifactorial nature of this tumor would be taken into account.