Abstract Background Outcome reporting in perianal fistulising Crohn’s disease (pfCD) remains variable, limiting the ability to compare studies, perform meta-analyses, and develop evidence-based, treat-to-target recommendations. We conducted an updated systematic review to characterise outcome domains and definitions currently used in pfCD interventional studies, as an initial step toward developing pragmatic targets for clinical care. Methods We updated a 2019 review1 to identify prospective studies (July 2016 to December 2024) that reported outcomes of medical or surgical interventions in 10 or more adults with pfCD. Ovid MEDLINE and EMBASE were searched, supplemented with studies that the IOIBD team had screened for their STRIDE III systematic review, specifically those with *fist* in the title or abstract. Two reviewers independently screened and extracted data through Covidence, focusing on definitions and tools used to assess clinical and radiological fistula response and remission. Results Of 1688 studies screened, 67 met inclusion criteria. Interventions included cellular therapies (34%), advanced medical therapies (25%), surgical treatments (16%), and combined approaches (9%). Clinical response measures, typically defined by absence or reduction of fistula discharge, were reported in 91% of studies, while radiological outcomes were included in 51%. Quality of life or patient-reported outcomes appeared in 42%. Seton removal was infrequently reported (16%), despite sometimes representing an important clinical milestone in fistula downstaging.2 Definitions varied widely. Clinical remission was most often defined as complete absence of discharge (67%), while closure of all external openings was less common (37%). Only one third of studies required durability of clinical response or remission across more than one visit. Radiological outcomes focused primarily on absence of collections (36%) or reduced inflammatory activity or fistula volume (33%), rather than complete tract closure. Conclusion Outcome reporting in pfCD remains inconsistent, with substantial variation in both clinical and radiological definitions of response and remission. These findings highlight the need to standardise pfCD-specific endpoints and outcome measures in order to support robust comparative studies and to strengthen evidence-based decision-making for pfCD. References: 1) Sahnan K, Tozer PJ, Adegbola SO, et al. Developing a core outcome set for fistulising perianal Crohn’s disease. Gut. 2019 Feb;68(2):226-238. 2) Hanna LN, Anandabaskaran S, Iqbal N, et al. Perianal Fistulizing Crohn’s Disease: Utilizing the TOpClass Classification in Clinical Practice to Provide Targeted Individualized Care. Clin Gastroenterol Hepatol. 2025 May;23(6):914-926. Conflict of interest: Dr. Hanna, Luke: None Joshi, Shivani: Speaker Fees from Lilly Sahnan, Kapil: Speaker fees from Takeda, JnJ, Intuitive Ad Board with Medtronic Yuan, Yuhong: No conflict of interest Jairath, Vipul: Consulting Fees: Abbvie, Alimentiv, Amgen, Anaptys Bio, Asahi Kasei, Asieris, Astra Zeneca, Attovia, Blackbird Labs, BMS, Boehringer Ingleheim, Biomebank, Caldera, Calluna, Catalytic Health, Celltrion, Ensho, Enthera, Exeliome Biosciences, Ferring, Fresenius Kabi, Gilead, Granite Bio, GSK, Janssen, Lilly, Merck, Mountainfield, MRM Health, Nxera, Organon, OSE Immunotherapeutics, Pendopharm, Pioneering Medicine, Pfizer, Prometheus, Roche/Genentech, Sanofi, SCOPE, Shattuck Labs, Sorriso, Spyre, Synedgen, Takeda, Teva, Tillotts, Union Therapeutics, Ventus, Ventyx, Vividion, Xencor, Zealand Pharma. Lung, Phillip FC: No conflict of interest Tozer, Philip: Personal Fees: Takeda - speakers fees, member of Inspire, and advisory boards Ferring - speakers fees Falk - speakers fees Tillott’s - speakers fees J & J - speakers fees Abbvie - speakers fees Hart, Ailsa: Grant: Takeda Personal Fees: Abbvie, Amgen, Arena, AZ, Falk, Celltrion, Eli Lilly, Ferring, Genentech/ Roche, GSK, Pfizer, Takeda, Napp, Pharmacosmos, Janssen (J & J), Bristol-Myers Squibb, Gilead, Galapagos, Alfasigma