Hyperinsulinaemia and hyperglycaemia are two possible risk factors for colorectal cancer, which constitutes the third leading cause of cancer death in Western countries. Molecular evidence as well as animal models provide support for these associations: Insulin has been shown to be an important growth factor for colonic carcinoma cells, and both insulin and insulin-like growth factor-1 receptors have been detected in colon cancer tissue. The insulin-signal transduction pathway is involved in the regulation of gene expression and apoptosis. The role of hyperglycaemia in carcinogenesis could include pathways via luminal factors (related to fecal bile acid concentrations, stool bulk, and prolonged transit time) or circulatory factors (via glucose as the only energy source for neoplastic cells). This review summarizes the epidemiologic literature with respect to hyperinsulinaemia and hyperglycaemia as risk factors for colorectal cancer, and aims to integrate the biological and epidemiological evidence. Epidemiologic findings to date indicate a slightly increased risk of colorectal cancer for diabetic patients; however, there are some inconsistencies. Possible explanations for these inconsistencies include inadequate information about patients' diabetic disease and treatment states. We suggest that future studies should take medical history, staging and treatment for hyperinsulinaemia and hyperglycaemia into account to further our understanding of the role of hyperglycaemia and hyperinsulinaemia in colorectal carcinogenesis.