Methods. We set up a single-center longitudinal observational study (LOS) planned to include 390 consecutive EPA patients observed over 5 years. EPA is defined as synovitis affecting 3 or more joints for more than one month and less than 12 months, with few specific exclusions. At inclusion, and at each pre-defined time points after disease onset, extensive (but focused) demographic, clinical, serological, radiological and genetic data are collected, without interference with their treatment. Treating physicians and patients remain uninformed about the status of the patients regarding research data (genomic data, anti-Sa and anti-CCP Abs). About 250 such patients will have been included at the time of renewal. Loss to follow up (up to V4 in some patients) at each visit is about 5% and is mostly found in patients in remission. Data collected are used to verify whether patients have reached predefined outcomes including remission, persistence of arthritis, persistence of arthritis fulfilling RA criteria, DMARD use, and SEVERE disease.