Introduction: Patients with poorly controlled diabetes mellitus may present repeatedly to the emergency department (ED) for management and treatment of hyperglycemic episodes, including diabetic ketoacidosis and hyperosmolar hyperglycemic state. The objective of this study was to identify risk factors that predict unplanned recurrent ED visits for hyperglycemia in patients with diabetes within 30 days of initial presentation. Methods: We conducted a one-year health records review of patients ≥18 years presenting to one of four tertiary care EDs with a discharge diagnosis of hyperglycemia, diabetic ketoacidosis or hyperosmolar hyperglycemic state. Trained research personnel collected data on patient characteristics and determined if patients had an unplanned recurrent ED visit for hyperglycemia within 30 days of their initial presentation. Multivariate logistic regression models using generalized estimating equations to account for patients with multiple visits determined predictor variables independently associated with recurrent ED visits for hyperglycemia within 30 days. Results: There were 833 ED visits for hyperglycemia in the one-year period. 54.6% were male and mean (SD) age was 48.8 (19.5). Of all visitors, 156 (18.7%) had a recurrent ED visit for hyperglycemia within 30 days. Factors independently associated with recurrent hyperglycemia visits included a previous hyperglycemia visit in the past month (odds ratio [OR] 3.5, 95% confidence interval [CI] 2.1-5.8), age <25 years (OR 2.6, 95% CI 1.5-4.7), glucose >20 mmol/L (OR 2.2, 95% CI 1.3-3.7), having a family physician (OR 2.2, 95% CI 1.0-4.6), and being on insulin (OR 1.9, 95% CI 1.1-3.1). Having a systolic blood pressure between 90-150 mmHg (OR 0.53, 95% CI 0.30-0.93) and heart rate >110 bpm (OR 0.41, 95% CI 0.23-0.72) were protective factors independently associated with not having a recurrent hyperglycemia visit. Conclusion: This unique ED-based study reports five risk factors and two protective factors associated with recurrent ED visits for hyperglycemia within 30 days in patients with diabetes. These risk factors should be considered by clinicians when making management, prognostic, and disposition decisions for diabetic patients who present with hyperglycemia.