Substantial evidence suggests that people with type 2 diabetes have an increased risk of developing several types of cancers. Insulin resistance, hyperinsulinemia, increased levels of IGF, elevated levels of steroid and peptide hormones, and inflammatory markers appear to play a role in the connection between them. Observational studies of these associations, including the potential role for glucose-lowering therapy, are being increasingly reported, but face a number of methodological challenges. This lecture will review the role of diabetes and its medications as risk factors for certain types of cancers, and their possible mechanisms.