Study objective Regionalized systems of trauma care and level verification are promulgated by the American College of Surgeons. Whether patient outcomes differ between the 2 highest verifications, Levels I and II, is unknown. In contrast to Level II centers, Level I centers are required to care for a minimum number of severely injured patients, have immediate availability of subspecialty services and equipment, and demonstrate research, substance abuse screening, and injury prevention. We compare risk-adjusted mortality outcomes at Levels I and II centers. Methods This was an analysis of data from the 2012 to 2014 Los Angeles County Trauma and Emergency Medical Information System. The system includes 14 trauma centers: 5 Level I and 9 Level II centers. Patients meeting criteria for transport to a trauma center are routed to the closest center, regardless of verification level. All adult patients (≥15 years) treated at any of the trauma centers were included. Outcomes of patients treated at Level I versus Level II centers were compared with 2 validated risk-adjusted models: Trauma Score–Injury Severity Score (TRISS) and the Haider model. Results Adult subjects (33,890) were treated at a Level I center; 29,724, at a Level II center. We found lower overall mortality at Level II centers compared with Level I, using TRISS (odds ratio 0.68; 95% confidence interval 0.59 to 0.78) and Haider (odds ratio 0.84; 95% confidence interval 0.73 to 0.97). Conclusion In this cohort of patients treated at urban and suburban trauma centers, treatment at a Level II trauma center was associated with overall risk-adjusted reduced mortality relative to that at a Level I center. In the subset of penetrating trauma, no differences in mortality were found. Further study is warranted to determine optimal trauma system configuration and allocation of resources.