OBJECTIVE Diabetic ketoacidosis (DKA) is a life-threatening but preventable complication in people with type 1 diabetes. We aimed to quantify the incidence of DKA according to age and describe the time trend of DKA among adults with type 1 diabetes in Denmark. RESEARCH DESIGN AND METHODS Individuals aged ‡18 years with type 1 diabetes were identified from a nationwide Danish diabetes register. Hospital admissions due to DKA were ascertained from the National Patient Register. The follow-up period was from 1996 to 2020. RESULTS The cohort consisted of 24,718 adults with type 1 diabetes. The incidence rate of DKA per 100 person-years (PY) decreased with increasing age for both men and women. From 20 to 80 years of age, the DKA incidence rate decreased from 3.27 to 0.38 per 100 PY. From 1996 to 2008, the incidence rate of DKA increased for all age-groups, with a subsequent minor decrease in incidence rate until 2020. From 1996 to 2008, the incidence rates increased from 1.91 to 3.77 per 100 PY for a 20-year-old individual and from 0.22 to 0.44 per 100 PY for an 80-year-old individual living with type 1 diabetes. From 2008 to 2020 the incidence rates decreased from 3.77 to 3.27 and from 0.44 to 0.38 per 100 PY, respectively. CONCLUSIONS The incidence rates of DKA are declining for all ages, with an overall decline from 2008 for both men and women. This likely reflects improved diabetes management for individuals with type 1 diabetes in Denmark.