Objective: This study aimed to investigate the clinical characteristics of newly diagnosed diabetic patients admitted with DKA in a tertiary care hospital. Methods: We performed a retrospective analysis of hospital admissions for DKA in people with newly diagnosed diabetes age > 18 years admitted to the department of internal medicine in Chung-ang University Hospital between January 2011 and December 2018. Patients with secondary diabetes from pancreatic disease or drug-induced diabetes were excluded. DKA was defined as an arterial pH level < 7.3, initial blood glucose > 13 mmol/L, serum bicarbonate level of < 15 mEq/L and ketonemia or ketonuria. Demographic and laboratory data, total hospitalization length of stay (days), ICU length of stay (hours), and discontinuation of insulin treatment were analyzed. Results: A total of 34 patients were included in this study. There were 20 (58.8%) males and 14 (41.2%) females. The mean age at onset of DKA was 41.5 + 16.4 years with a range from 19 to 88 years. Among 34 patients, 12 patients continued insulin treatment after 3.7 months. The patients were younger and more obese. They had higher glucose level and more preserved beta cell function at admission. In 22 patients who continued with insulin treatment, 7 patients were suitable for fulminant type 1 diabetes, with the presence of initial HbA1c level < 8.5%, duration of hyperglycemic symptoms < 7 days, and c-peptide < 0.05 ng/mL. Total hospitalization and ICU length of stay were not different among 3 groups, however, the patients with ketosis-prone type 2 diabetes mellitus showed a rather long tendency. Conclusion: There was much heterogeneity in new-onset diabetic patients presenting with diabetic ketoacidosis. Typical type 1 diabetes mellitus was not major type, and fulminant type 1 diabetes mellitus and ketosis-prone type 2 diabetes mellitus were not uncommon in our study.