We investigated the phenotypic diversity caused by biallelic loss-of-function ZNF808 variants by screening a cohort of 4699 individuals with genetically undiagnosed monogenic diabetes: 335 with neonatal diabetes (NDM, diagnosed <6 months), 194 with infancy-onset diabetes (diagnosed 6–12 months) and 4170 diagnosed with diabetes between 1 and 60 years of age. Here, ZNF808 is linked to neonatal diabetes mellitus.