Objectives. The prehospital management of trauma patients remains controversial. Little is known about the time each procedure contributes to the on-scene duration, and this information would be helpful in prioritizing which procedures to perform in the prehospital setting. We sought to estimate the contribution of procedures to on-scene duration focusing on intubation and establishment of intravenous (IV) access. Methods. Data were provided by the Office of Emergency Planning and Response at the Mississippi Department of Health. Real-time prehospital patient-level data are collected by emergency medical services (EMS) providers for all 9-1-1 calls statewide. Linear regression was performed to determine the overall additional time for an average procedure and to calculate marginal increases in on-scene time associated with the establishment of IV access and with endotracheal intubation. Analyses were performed using Stata 9. Results. During 2001–2005, 192,055 prehospital runs were made for trauma patients. 121,495 (63%) included prehospital procedures. Average on-scene duration for those runs was 15:24 (minutes:seconds). On average, each procedure was associated with an addition of 1 minute to the on-scene duration (95% confidence interval [CI]: 58–62 seconds). A scene involving the establishment of IV access was 5:04 longer, while one involving tracheal intubation was 2:36 longer. Conclusions. We estimate the marginal increase in on-scene duration associated with the performance of an average procedure, establishment of IV access, and endotracheal intubation. There are policy and planning implications for the time trade-off of prehospital procedures, especially discretionary ones. Press coverage: http://www.jems.com/article/cardiac-circulation/how-much-do-ems-procedures-cos-0