The aims of this study were to estimate incidence of diabetic ketoacidosis and mortality from diabetic ketoacidosis using data from public health registries. Four thousand eight hundred and seven admissions in the period 1996-2002 and 137 deaths in the period 1996-2000 with a diagnosis of diabetic ketoacidosis were identified from the Danish National Patient Registry and Danish Cause of Death Registry, respectively. Annual incidence of diabetic ketoacidosis in the general population was estimated to 12.9 per 100,000, being higher in males than in females (14.4 versus 11.4 per 100,000, p<0.0001). Twelve percent of all patients were classified as Type 2 diabetes, predominantly in patients >50 years. Overall mortality was 4%, being higher in patients >70 years than in patients < or =70 years (15% versus 2%, p<0.0001). One or more additional somatic diagnoses were stated on 77% of the death certificates, most often a diagnosis of cardiovascular (47%) or infectious (30%) diseases. Compared to previous studies, the incidence in the general population seems to have remained unaltered the past 25 years, but may have decreased in younger patients. Older patients with diabetic ketoacidosis differed from younger patients in having a higher mortality and a larger proportion of patients classified as Type 2 diabetes.