Introduction: Mass casualty incidents, specifically incidents with chemical, biological, radiological, and nuclear agents (CBRN) or terrorist attacks, challenge medical coordination, rescue, and ambulance care. Recently in the Netherlands, a new model for emergency preparedness for large-scale mass casualties and a specific approach dealing with terrorist attacks was introduced (2016). Aim: To provide insight into the first experiences with this approach in order to identify strengths and pitfalls. Methods: The study had a qualitative design and was performed between January 2017 and June 2018. A semi-structured interview included topics that were selected based on available literature. All interviews were typed out verbatim and were analyzed using a structured approach of labeling and clustering of the response. Results: The main issues raised by the respondents included the following: The interpretation of definitions introduced in the new model for the mass casualty preparedness model and the terrorist attack approach differed among respondents. All respondents supported the six points of departure in the CRBN and terrorist attack approach. Awareness of optimal personal safety (‘safety first principle’) specific for CBRN and terrorism is lacking. Respondents reported that several rescue workers did not feel competent to perform specific newly introduced tasks, such as the command and control of the first ambulance arriving at the scene and the coordination task of emergency transport by the dispatch nurse. Current regional differences in preparedness may complicate interregional collaboration. Discussion: As the approach is new and experience is primarily based on the outcome of exercises, the systematic planning and evaluation of exercises, and sharing of opinions and knowledge, as a result, is important to ensure an unambiguous approach in a real situation.