Abstract Disclosure: C.A. Percy: None. A. Turner: None. L. Aphramor: None. D. Broom: None. C. Clark: None. F. Martin: None. P. Wark: None. Introduction: Polycystic ovary syndrome (PCOS) has significant impact on depression, anxiety, psychological wellbeing and health-related quality of life. We co-created a theory-led, evidence-based, 6-week, digital self-management and positive wellbeing intervention (Hope PCOS), delivered to UK adults. We tested the intervention’s potential to improve mental health and wellbeing outcomes and its acceptability and usability for adults living with PCOS. Methods: This was a mixed methods feasibility randomised controlled trial conducted online, with a pre-post, waitlist-controlled design. Primary outcomes were recruitment, completion (≥ 3 intervention sessions) and follow-up rates. At baseline, participants reported demographic information, PCOS symptoms, depression (Patient Health Questionnaire (PHQ-9)), anxiety ((Generalised Anxiety Disorder Assessment (GAD-7)), polycystic ovary syndrome health-related quality of life (PCOSQ-50), psychological wellbeing (Warwick-Edinburgh Mental Wellbeing Scale, WEMWBS) and self-efficacy (Self-Efficacy to Manage Chronic Disease Scale (SEMCD6)) before randomisation to an intervention group (IG) receiving the intervention immediately or a waitlist control group (CG) receiving the intervention 12 weeks later. PHQ-9, GAD-7, PCOSQ-50, WEMWBS and SEMDC6 were reassessed at 6 and 12 weeks. IG participants reported the usability of the digital intervention (system usability scale (SUS)) and acceptability via qualitative exit interviews. Results: Of 131 eligible, consented participants, 83% (N=109, age M=37.1, SD=8.6 years) completed baseline measures and were randomised to the IG (n=54) or the CG (n=55). Baseline clinical caseness was high for depression (n=77, 70.6%) and anxiety (n=78, 71.6 %). Twenty-one participants (39%) in the IG completed ≥3 intervention sessions. At 6-week follow-up, completion of secondary outcomes was n=32 (59%) for IG and n= 38 (69%) for CG; at 12 weeks, n=31 (57%) for IG and n= 38 (69%) for CG. Twelve IG participants took part in the exit interviews. Exploratory descriptive statistics suggest there were greater improvements in depression, anxiety, psychological wellbeing, self-efficacy and quality of life for the intervention group completers compared to the waitlist control group. SUS data and thematic analysis suggest the intervention was usable, acceptable, relevant and interesting. Participants reported experiences including feeling seen and valued, having the difficulties of lifestyle change acknowledged, and learning valuable lessons, particularly how to monitor and manage emotions, prioritise self-care and complete personal goals. Conclusions: This novel intervention was rated as usable and acceptable, with potential for improving mental health and wellbeing outcomes. More research is needed to identify for whom the intervention is beneficial and on implementation in practice. Presentation: 6/1/2024