Background:The specialty of emergency medical services (EMS) medicine focuses on providing out-of-hospital patient care, including initial stabilization, treatment, and transport in specially equipped vehicles including ambulances and airframe platforms to hospitals and better-resourced destinations. The Core Content of EMS Medicine outlines the knowledge, procedures, and psychomotor skills relevant to prehospital patient care. However, this document does not specify the high-consequence skills that are infrequently performed and that carry high levels of complexity as well as potential morbidity. We refer to these as high-acuity low-occurrence (HALO) skills. Additionally, there is no consensus definition of what meets the criteria for a HALO skill. The goals of this pilot study were twofold: (1) to determine a consensus definition for a HALO skill and (2) to survey EMS fellowship faculty to identify an initial set of EMS physician trainee skills that meet the HALO definition. Methods: Using a modified Delphi method, we established a consensus definition of a HALO skill as well as skills that met this definition for EMS physicians. Demographic information was collected from the experts. Results: There was 100% agreement in the definition provided of a HALO skill. No additional proposed definitions were provided. Thirteen HALO skills were suggested by the panel from the originally proposed 56 skills, requiring three rounds to establish consensus. Final skill domains emphasized by the expert panel include airway management, obstetric emergencies, and shock management. Conclusions: We present an initial consensus definition of a HALO skill and a recommended list of HALO skills for EMS physicians in training. Opportunity exists for further research to validate the definition and list of HALO skills through the sampling of a broader group of EMS physicians.