Introduction: Diabetes mellitus is an increasingly prevalent chronic condition that is usually managed in an outpatient setting. However, the emergency department (ED) plays a crucial role in the management of diabetic patients, particularly for those who are presenting with newly diagnosed diabetes. Little research has been done to characterize the population of patients presenting to the ED with hyperglycemia with no previous diagnosis of diabetes. The objective of this study was to describe the epidemiology, treatment, and outcomes of patients who were newly diagnosed with diabetes in the ED and to compare those with newly diagnosed type I versus type II diabetes. Methods: A one-year health records review of newly diagnosed diabetes patients ≥18 years presenting to one of four tertiary care EDs was conducted. All patients with a discharge diagnosis of hyperglycemia, diabetic ketoacidosis or hyperosmolar hyperglycemic syndrome were screened, but only those who did not have a previous history of diabetes were included. Trained research personnel collected data on patient characteristics, management, disposition, and outcome. Descriptive statistics were used to summarize the data where appropriate. Results: Of 645 patients presenting with hyperglycemia in the study period, 112 (17.4%) were newly diagnosed diabetes patients. Of these patients, 30 (26.8%) were later diagnosed with type I diabetes and 82 (73.2%) were diagnosed with type II diabetes. For the newly diagnosed type I patients the mean (SD) age was 27.6 (9.9) and the mean (SD) age for type II patients was 52.4 (14.1). Of all the new onset patients, 26.8% were diagnosed with diabetic ketoacidosis. The percentage of patients diagnosed with diabetic ketoacidosis was higher in type I than type II (63.3% vs 13.4%; P<0.01). A total of 49 (43.8%) patients were admitted to the hospital, and more patients with type I were admitted compared to those with type II (66.7% vs 35.4 %; P<0.01). Conclusion: Limited research has been done to describe patients newly diagnosed with diabetes in the ED. Patients with type I were found to be more likely to present to the ED with serious symptoms requiring admission to hospital. Our findings demonstrate that the ED may have a strong potential role for improving diabetic care, by providing future opportunities for education and follow-up in the ED to reduce complications, particularly in type I.