Objectives: The European League Against Rheumatism (EULAR) and the European Federation of National Associations of Orthopaedics and Traumatology (EFORT) have recognised the importance of variation in diagnostic and therapeutic performance across disciplines, have found consensus in starting task forces aiming at achieving diagnostic and therapeutic uniformity, and have identified medical conditions with which representatives of both organisations will frequently be confronted in common clinical practice. The aim of the present work was to establish recommendations for the diagnosis and initial management of patients presenting with acute or recent onset swelling of the knee. Methods: The EULAR standard operating procedures for the elaboration and implementation of evidence-based recommendations were followed. Results: In all, 11 rheumatologists from 11 countries and 12 orthopaedic surgeons from 7 countries met twice under the leadership of 2 conveners, a clinical epidemiologist and a research fellow. After carefully defining the content and procedures of the task force, research questions were developed, a comprehensive literature search was performed and the results were presented to the entire committee. Subsequently, a set of 10 recommendations was formulated based on evidence from the literature if available, and after discussion and consensus building. Conclusions: This is the first combined interdisciplinary project of rheumatologists and orthopaedic surgeons, successfully aiming at achieving consensus in the diagnosis and initial management of patients presenting with acute or recent onset swelling of the knee.