ObjectivesTo summarise incidence and prevalence of diabetic ketoacidosis (DKA) in adults with type 1 diabetes (T1D) for the overall patient population and different subgroups (age, sex, geographical region, ethnicity and type of insulin administration).DesignSystematic literature review (SLR).Data sourcesMedline (via PubMed) and Embase (1 January 2000 to 23 June 2016).Study selectionPeer-reviewed observational studies with reported data on the incidence or prevalence of DKA in T1D adults were included. A single reviewer completed the study screening and selection process and a second reviewer performed an additional screening of approximately 20% of the publications; two reviewers independently conducted the quality assessment; the results were narratively synthesised.ResultsOut of 1082 articles, 19 met the inclusion and exclusion criteria, with two additional studies identified that did not specify the patient age range and are therefore not included in the SLR. Overall, eight studies reported incidence with a range of 0–56 per 1000 person-years (PYs), with one outlying study reporting an incidence of 263 per 1000 PYs. Eleven studies reported prevalence with a range of 0–128 per 1000 people. Prevalence of DKA decreased with increasing age. Subgroup analyses were performed using data from no more than two studies per subgroup. There was a higher prevalence of DKA reported in women, non-whites and patients treated with insulin injections compared with men, whites and patients using continuous subcutaneous insulin infusion pumps, respectively.ConclusionsTo our knowledge, this is the first SLR on the epidemiology of DKA in T1D adults. Despite an increasing prevalence of T1D in recent years, DKA in adults has been poorly characterised. In an era when the benefit–risk profiles of new antidiabetic therapies are being evaluated, including the potential risk of DKA, there is a clear need to better elucidate the expected rate of DKA among T1D adults.