BACKGROUND: Seriously injured patients may benefit from prehospital interventions provided by a critical care physician. The relationship between case volume and outcome has been established in trauma teams in hospitals, as well as in prehospital advanced airway management. In this study, we aimed to assess if a volume-outcome relationship exists in prehospital advanced trauma care. METHODS: We performed a retrospective cohort study using the national helicopter emergency medical services database, including trauma patients escorted from scene to hospital by a helicopter emergency medical services physician during January 1, 2013, to August 31, 2019. In addition, similar cases during 2012 were used to determine case volumes. We performed a multivariate logistic regression analysis, with 30-day mortality as the outcome. Age, sex, Glasgow Coma Scale, shock index, mechanism of injury, time interval from alarm to the patient and duration of transport, level of receiving hospital, and physician's trauma case volume were used as covariates. On-scene times, interventions performed, and status at hospital arrival were assessed in patients who were grouped according to physician's case volume. RESULTS: In total, 4,032 escorted trauma patients were included in the study. The median age was 40.2 (22.9-59.3) years, and 3,032 (75.2%) were male. Within 30 days, 498 (13.2%) of these patients had died. In the highest case volume group, advanced interventions were performed more often, and patients were less often hypotensive at handover. Data for multivariate analysis were available for 3,167 (78.5%) of the patients. Higher case volume was independently associated with lower mortality (odds ratio, 0.59; 95% confidence interval, 0.38-0.89). CONCLUSION: When a prehospital physician's case volume is higher in high-risk prehospital trauma, this seems to be associated with more active practice patterns and significantly lower 30-day mortality. The quality of prehospital critical care could be increased by ensuring sufficient case volume for the providers of such care. LEVEL OF EVIDENCE: Prognostic and Epidemiologic; Level III.