Information on the occurrence of colon cancer, as with other cancers, has historically been meager. Indeed, accurate information at its current frequency, through cancer registries, has only relatively recently become available. The disease is certainly rare in rural, less developed populations. In urban populations in transition and in developed populations, however, its epidemiology presents many puzzles. In both contexts, some rates are higher and others are lower than would be expected. This points to the existence and operation of as-yet-undefined promotive and inhibiting factors. Uncertainties as to the identity and weight of risk factors thus complicate the task of seeking to prevent or to ameliorate the disease. Apart from genetic influences, it is possible that factors such as the chemistry and microbiology of the gastrointestinal tract, the proportion of resistant starch reaching the large bowel, and the fecal pH of digestra during its traverse are among the determinants.