This review summarizes advances in our understanding of the structure and function of the ATP-sensitive potassium (K(ATP)) channel of the pancreatic beta-cell that have been made over the last 5 years. It discusses recent structural studies of the octameric K(ATP) channel complex and studies of the regulation of K(ATP) channel activity by nucleotides. It then considers the molecular mechanism by which gain-of-function mutations in the Kir6.2 subunit of the K(ATP) channel reduce channel inhibition by ATP and thereby lead to neonatal diabetes, and how identification of these mutations has led to changes in therapy. Finally, it illustrates how mouse models of glucose intolerance or diabetes can provide fresh insight into beta-cell function, using the C57BL/6J mouse, whose glucose intolerance arises from mutations in nicotinamide nucleotide transhydrogenase, as an example.