There is continuous drive to optimize healthcare for the most severely injured patients. Although still under debate, a possible measure is to provide 24/7 in-house (IH) coverage by trauma surgeons. The aim of this study was to compare process-related outcomes for severely injured patients before and after transition of attendance policy from an out-of-hospital (OH) on-call attending trauma surgeon to an in-house attending trauma surgeon.Retrospective before-and-after study using prospectively gathered data in a Level 1 Trauma Center in the Netherlands. All trauma patients with an Injury Severity Score (ISS) >24 presenting to the emergency department for trauma before (2011-2012) and after (2014-2016) introduction of IH attendings were included. Primary outcome measures were the process-related outcomes Emergency Department length of stay (ED-LOS) and time to first intervention.After implementation of IH trauma surgeons, ED-LOS decreased (p = 0.009). Time from the ED to the intensive care unit (ICU) for patients directly transferred to the ICU was significantly shorter with more than doubling of the percentage of patients that reached the ICU within an hour. The percentage of patients undergoing emergency surgery within 30 min nearly doubled as well, with a larger amount of patients undergoing CT imaging before emergency surgery.Introduction of a 24/7 in-house attending trauma surgeon led to improved process-related outcomes for the most severely injured patients. There is clear benefit of continuous presence of physicians with sufficient experience in trauma care in hospitals treating large numbers of severely injured patients.