Aim The aim of the study was to analyse the prevalence of diabetic onset ketoacidosis (DKA) during a period of 20 years (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)) on a population basis in the whole of Austria. Methods A prospective population-based incidence study (1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008) was performed. The registered data set comprised blood glucose, pH, ketonuria and clinical symptoms of DKA at manifestation. DKA was defined as pH<7.3 and severe DKA as pH<7.1. Time trends were estimated using linear regression models. Results During the study period, 3331 children <15 years of age (1,797 boys and 1,534 girls) were registered with newly diagnosed type 1 diabetes. Of these, 1,238 (37.2%) presented with DKA, 855 (25.7%) had a mild and 383 (11.5%) a severe form, and one patient died at onset. DKA frequency was negatively associated with age at onset (p< 0.0001). In children <2 years the prevalence was 60%, with a higher risk for girls (70% vs 54% for boys, p<0.05). Despite a significant increase in diabetes incidence in Austria during the observation period from 8.4 to 18.4/ 100,000 (p<0.0001), no significant change in the prevalence of DKA at manifestation was observed. Conclusions The overall frequency of DKA in children with newly diagnosed type 1 diabetes in Austria is high and has not changed during the last 20 years despite a clear increase in the manifestation rate. In particular, children less than 2 years of age have a high risk of DKA at onset.