Background <p>Prehospital Assessment Units were recently introduced to emergency medical services in Denmark. These units are designed to assess, triage, and treat patients on-site, and either release, refer to alternative care pathways, or arrange hospital conveyance. The initiative has increased the need for effective collaboration among healthcare professionals in acute care services, including paramedics, nurses, and physicians in emergency medical services, municipalities, emergency departments, and general practice. This study investigates Relational Coordination among healthcare professionals involved in this task for patients triaged by the Prehospital Assessment Units in the Region of Southern Denmark.</p> Methods <p>A mixed-methods study, inspired by a convergent parallel design, was conducted based on the framework described in the theory of Relational Coordination. This theory highlights the importance of Communication (Frequent Communication, Timely Communication, Accurate Communication, and Problem-Solving Nature of Communication) and Relationships (Shared Goals, Shared Knowledge, and Mutual Respect). Data were collected between April and August 2024 via online questionnaires and in June 2024 through focus groups.</p> Results <p>Questionnaire responses from 138 healthcare professionals were analysed, and 18 participated in the focus groups. Most collaborative ties were classified as moderate and strong. However, weaker ties were identified in Timely Communication and Frequent Communication, and Shared Knowledge, highlighting challenges in both dimensions of Relational Coordination. The qualitative analysis produced four themes: 1) <i>Insufficient communication </i> due to low quality or lack of written communication, 2) <i>Navigating care through phone calls </i>to share information, 3) <i>Multiple objectives with hindered observers</i>, driven by the coexistence of different objectives of the unit and limited insight into the whole care pathway, and 4) <i>Interprofessional tensions in acute care collaboration</i>, based on challenges regarding the competencies, incentives, roles and responsibilities required to achieve the best care pathway for each patient.</p> Conclusion <p>The collaboration among healthcare professionals for patients triaged by the Prehospital Assessment Unit was generally classified as moderate to strong. However, critical challenges were identified. Optimising task assignments, enabling municipal correspondence, and addressing discrepancies in objectives, competencies, and roles may improve collaboration. These findings point to broader lessons for strengthening prehospital and inter-organisational coordination internationally, where challenges of information flow, role clarity, and mandate alignment are common.</p>