We assessed the incidence of diabetic ketoacidosis (DKA) in children aged <15 years with newly diagnosed type 1 diabetes mellitus (T1DM) in the Auckland Region (New Zealand) in 1999-2013, in a retrospective review of a complete regional cohort. DKA and its severity were classified according to ISPAD 2014 guidelines. Of 730 children presenting with new-onset T1DM over the 15-year time period, 195 cases had DKA of any severity (27%). There was no change in the incidence of DKA or the proportion of children with severe DKA at presentation. The incidence of DKA among children aged <2.0 years (n = 40) was 53% compared to 25% for those aged 2-14 years (n = 690; p = 0.005). In children aged 2-14 years, increasing age at diagnosis was associated with greater likelihood of DKA at presentation (p = 0.025), with the odds of DKA increasing 1.06 times with each year increase in age. Non-Europeans were more likely to present in DKA than New Zealand Europeans (OR 1.52; p = 0.048). Despite a consistent secular trend of increasing incidence of T1DM, there was no reduction in the incidence of DKA in new-onset T1DM in the Auckland Region over time. Thus, it is important to explore ways to reduce DKA risk.