A fundamental goal of continuous process improvement programs is to evaluate and improve the ratio of actual to expected mortality. To study this, we examined contributors to error-associated deaths during two consecutive periods from 1996 to 2004 (period 1) and 2005 to 2014 (period 2). All deaths at a level I trauma center with an anticipated probability of death less than 50% and/or identified through process improvement committees were examined. Demographics were assessed for trend only because period 1 data were only available in median and interquartile range. Each death was critically appraised to identify potential error, with subsequent classification of error type, phase, cause, and contributing cognitive processes, with comparison of outcomes made using χ test of independence. During period 1, there were a total of 44,401 admissions with 2,594 deaths and 64 deaths (2.5%) associated with an error, compared with 60,881 admissions during period 2 with 2,659 deaths and 77 (2.9%) associated with an error. Deaths associated with an error occurred in younger and less severely injured patients in period 1 and were likely to occur during the early phase of care, primarily from failed resuscitation and hemorrhage control. In period 2, deaths occurred in older more severely injured patients and were likely to occur in the later phase of care primarily because of respiratory failure from aspiration. Despite injured patients being older and more severely injured, error-associated deaths during the early phase of care that was associated with hemorrhage improved over time. Successful implementation of system improvements resolved issues in the early phase of care but shifted deaths to later events during the recovery phase including respiratory failure from aspiration. This study demonstrates that ongoing evaluation is essential for continuous process improvement and realignment of efforts, even in a mature trauma system. Therapeutic/Care Management, level IV.