- Background Diabetic ketoacidosis (DKA) occurs most often in patients with type 1 diabetes, however patients with type 2 diabetes are also susceptible to DKA under stressful conditions. The aims of our study were to evaluate and compare the clinical and biochemical characteristics and outcomes of type 1 versus type 2 diabetes mellitus (DM) patients with DKA. Methods A retrospective cohort study of adult patients hospitalized with DKA between January 1, 2003, and January 1, 2010. The clinical and biochemical characteristics of DKA patients with type-1 DM were compared with those of patients with type-2 DM. The primary outcome was in-hospital all-cause mortality. Results The study cohort included 201 consecutive patients for whom the admission diagnosis was DKA: 166 patients (82.6%) with type-1 DM and 35 patients (17.4%) with type-2 DM. The patients with DKA and type-2 DM were significantly older than patients with type-1 DM (64.3 versus 37.3, P < 0.001). Significantly more patients with severe forms of DKA were seen in the group with type-2 DM (25.7% versus 9.0%, P = 0.018). The total in-hospital mortality rate of patients with DKA was 4.5%. The primary outcome was significantly worse in the group of patients with type-2 DM. Conclusions DKA in patients with type-2 DM is a more severe disease with worse outcomes compared with type-1 DM. Advanced age, mechanical ventilation and bed-ridden state were independent predictors of 30-day mortality.