Background: Supervised group exercise (SGE) for people with axSpA is widely available in the Netherlands [1]. Its contents have barely changed over the past 30 years, despite new evidence-based insights to improve the quality of SGE [1,2]. Objectives: To evaluate the process and effect of the implementation of enhancements in SGE for people with axSpA in the Netherlands. Methods: This implementation study was executed in four regions, organising nine axSpA-specific SGE classes. The implemented enhancements included: 1. Exercise personalisation based on periodic assessments, including the 6-Minute Walk Test (6MWT) and the Ankylosing Spondylitis Performance Index (ASPI; improved/not improved); 2. High intensity aerobic exercise including intensity monitoring (e.g. by heartrate or BORG-scale); 3. Group education on home exercise and physical activity (e.g. promotion of an app). The implementation strategy was executed over a period of one year and consisted of a one-day training for the supervisors and bimonthly telephone support. To evaluate the implementation effect, a survey was sent to 95 SGE participants, including two questions evaluating changes in the programme and in own functioning, as well as the ‘ASAS Health Index’ (ASAS HI) and the ‘Short Questionnaire to Assess Health-enhancing physical activity’ (SQUASH), which were also administered at baseline. In addition, the data from the periodic assessments (6MWT and ASPI) were used. Changes were analysed with the Wilcoxon Signed-Rank Test. To evaluate the implementation process, apart from specific questions in the patient survey, semi-structured interviews with supervisors from each region were conducted. Results: The survey was returned by 60/95 (63%) SGE participants (72% male, median age 60 years). Effects: As shown in Table 1, 33% experienced improved functioning, 37% improved performance on ASPI and the improvements on 6MWT were statistically significant, p < .05, whereas there were no significant changes in ASAS HI and SQUASH. Table 1. SGE ...