m>HNF1Am> gene mutations are the most common cause of maturity-onset diabetes of the young (MODY) in the UK. Persons with HNF1A–MODY display sensitivity to sulphonylurea therapy; however, the long-term efficacy is not established. There is limited literature as to the prevalence of micro- and macrovascular complications in this unique cohort. The aim of this study was to determine the natural progression and clinical management of HNF1A–MODY diabetes in a dedicated MODY clinic.