Strong correlations among countries between per capita dietary fat consumption and rates of cancers of the breast, colon, and rectum have suggested possible causal relationships. However, in large prospective studies, total fat intake has not been associated with risk of breast cancer, suggesting that the international correlations are seriously confounded by differences in other variables related to affluence, including reproductive variables, physical activity, and food availability. For colon and prostate cancer, the data from prospective studies are more limited, but also suggest that fat per se is not a risk factor. High red meat consumption may be related to risk of colon cancer independent of total fat intake, and some factor associated with consumption of animal fat, but not vegetable fat, appears to be related to risk of prostate cancer. Excess body fat, which is determined by the balance between physical activity and energy intake from all sources, is an important cause of post-menopausal breast cancer and probably colon cancer. These developments suggest that international comparisons of diets and disease rates should be interpreted cautiously and may be highly misleading.