HNF1B and neonatal diabetes mellitus: While maturity-onset diabetes of the young type 5 is a well-recognized manifestation, neonatal diabetes mellitus (NDM) associated with HNF1B is exceedingly rare, and has only been reported in patients harboring single nucleotide variants.<h4>Case presentation</h4>We describe two unrelated female children presenting with transient NDM caused by a complete HNF1B gene deletion.