The American College of Surgeons Committee on Trauma defines undertriage (UT) as any major trauma patient (injury severity score ≥ 16) not undergoing treatment at the highest level of trauma team activation. This methodology does not account for many important factors that may impact outcome. We performed a retrospective review of the Pennsylvania State Trauma Registry to determine the impact of treatment interventions on mortality. Patients were stratified by triage category as follows: UT, appropriate triage, and overtriage. Multiple prehospital (PH) and ED interventions were assessed. Increased mortality was observed in all triage groups in patients requiring intervention. A logistic regression analysis was performed to assess the independent effect of individual interventions on mortality for patients triaged to partial activation or consult. PH CPR (OR 66.13 [47.07-92.93]), ED CPR (OR 16.87 [8.82-32.27]), PH or ED intubation (OR 16.68 [13.90-20.03]), PH or ED packed red blood cell transfusion (OR 1.89 [1.54-2.33]), emergent operative intervention (OR 3.58 [3.07-4.19]), ED central venous access (OR 5.04 [2.31-10.97]) were all associated with worsening mortality. The American College of Surgeons Committee on Trauma methodology overestimates mortality risk when emergent interventions are not required and underestimates risk where such interventions are necessary. Future methodologies for assessing UT should include these interventions.