Introduction: Many patients leave the Emergency Department (ED) before beginning or completing medical evaluation. Some of these patients may be at higher medical risk depending on their timing of leaving the ED. The objective of this study was to compare patient, hospital, and visit characteristics of patients leaving prior to completing medical care in the ED either before or after evaluation by a medical provider. Methods: This is a retrospective cross-sectional analysis of ED visits using the 2009-2011 National Hospital Ambulatory Medical Care Survey. The target population was identified by coded dispositions corresponding to leaving prior to completing medical care, and two groups were defined based on whether or not they had been evaluated by a medical professional. Data are reported as means (with standard errors) and proportions, and bivariate and multivariate logistic regressions were performed. All analysis was performed using SAS 9.4 and SUDAAN 11.0.1 to account for the complex sample design. Results: 100,962 ED visits were documented from 2009-2011, representing a weighted count of 402,211,907 total ED visits. 2,646 (3%) resulted in a disposition of left without completing medical care. Of these visits, 1,792 (68%) left prior to being seen by a medical provider versus 854 (32%) who left after medical provider evaluation. Patients who left after being assessed by a medical provider were older, had higher acuity visits, were more likely to have visited an ED without nursing triage, more likely to have arrived by ambulance, and more likely to have private insurance than other payment arrangements (e.g. worker’s compensation or charity). Conclusion: When comparing all patients who left the ED prior to completion of care, those who left after versus before medical provider evaluation differed in their patient, hospital, and visit characteristics and may represent a high risk patient group.