<h3>Background:</h3> In 2021 we described the baseline clinical information about 887 FMF patients enrolled in the Eurofever registry since 2009. <h3>Objectives:</h3> We describe now first longitudinal data about these patients. <h3>Methods:</h3> Patients with FMF enrolled in Eurofever registry with at least one follow-up visit were included in a longitudinal study. Demographic and clinical data were analyzed. Disease activity and maximum dose of colchicine were defined according to the 2016 EULAR recommendation [1]. <h3>Results:</h3> 1104 patients with FMF are enrolled in Eurofever registry in November 2023, 574 males and 530 females. The median age at disease onset was 3.8 (0.4 - 28.1); the median diagnostic delay was 2.4 (0.1 – 28.7); the median age at enrollment was 7.9 (1.7 – 50.8). Follow-up information was available in 497 patients, with a mean number of follow-up visits of 2.2 (25th-75th centile 1-4) and a mean duration of follow-up of 5.4 years (range 2.2 – 8.2). At the last follow-up around half of patients in the longitudinal cohort were in complete remission, 34.9% experienced some disease activity (&lt;1 episode/month) while only 9.2% experienced ≥ 1 episode/month and are therefore considered resistant to treatment according to the 2016 EULAR Guidelines (Table 1). At last follow-up visit 85.9% of patients of the longitudinal cohort were receiving colchicine, with a median duration of treatment of 4.4 years (0.4 – 15.4). Among resistant patients only 1 reached maximum recommended dose per age of colchicine according EULAR Guidelines (2 patients in partial remission, only 3 patients in complete remission). 8.2% of patients were on canakinumab while 0.4% were receiving anakinra. Among patients receiving biological treatments, 35 (81.4%) were receiving a combination of colchicine and biologics. Rate of withdrawal for colchicine were 10.3%, for canakinumab 6.5% while for anakinra was higher (61.1%). Reasons for withdrawal of treatment are detailed in Table 2. <h3>Conclusion:</h3> This study analyzes the initial data concerning the natural history of the Eurofever FMF cohort. At the last follow-up less than 50% of the patients have achieved complete disease control. Colchicine is the most used treatment. Among biologic drugs, IL-1 inhibitors are the most frequently used, with a good treatment retention rate at the last follow-up, especially for anti-IL-1 monoclonal antibody. <h3>REFERENCES:</h3> [1] S. Ozen <i>et al.</i>, "EULAR recommendations for the management of familial Mediterranean fever," doi: 10.1136/annrheumdis-2015-208690. <h3>Acknowledgements:</h3> This study is supported by a research collaboration agreement with Novartis. <h3>Disclosure of Interests:</h3> Marta Bustaffa: None declared, Gayane Amaryan: None declared, Romina Gallizzi: None declared, Efimia Papadopoulou-Alataki: None declared, Maria Carrabba: None declared, Jordi Antón: None declared, Gabriele Simonini: None declared, Maria Alessio: None declared, Luciana Breda: None declared, Jasmin B. Kuemmerle-Deschner: None declared, Donato Rigante: None declared, Laura Obici: None declared, Antonella Insalaco: None declared, Elizabeth Legger: None declared, Roberta Caorsi: None declared, Nicolino Ruperto Abbvie, Aclaris, Amgen, AstraZeneca, Aurinia, BMS, Boehringer Ingelheim, Eli Lilly, Galapagos, Guidepoint, Janssen, Novartis, Pfizer, Sanofi, Marco Gattorno Novartis, Sobi, Seza Ozen: None declared.

POS0157 THE EUROFEVER FMF LONGITUDINAL COHORT: FIRST LONGITUDINAL DATA