Maturity-onset diabetes of the young (MODY) is a rare subtype of type 2 diabetes that is characterized by autosomal-dominant inheritance and can be caused by mutations in hepatocyte nuclear factor 4alpha (HNF-4alpha). Odom and colleagues have combined chromatin immunoprecipitation with promoter microarrays to identify numerous promoters occupied by HNF-4alpha in the human liver and islet, suggesting a very broad role for HNF-4alpha in glucose homeostasis. This notion is supported by recent genetic studies linking HNF-4alpha to the much more common late-onset type 2 diabetes.