Pouch-related fistulae, such as pouch-anal and pouch-vaginal fistulae, are serious complications that impact ⁓5% of patients undergoing ileoanal pouch surgery, frequently leading to pouch failure. Research on treatment options is limited by small studies with inconsistent outcome reporting. To address this, the Pouch Anal and Vaginal Fistula Core Outcome Set (PAVFCOS) was developed, identifying seven key outcomes through stakeholder consensus. This study aims to create a core outcome measurement set (PAVFCOMS) to standardize how outcomes are measured in pouch fistula treatment, in line with Consensus-based Standards for the Selection of Health Measurement Instruments (COSMIN) guidelines. PAVFCOMS will incorporate validated patient-reported (PROMs) and clinician-reported (ClinROMs) outcome measures to provide a standardized tool for future clinical research. The study follows a two-phase process per COSMIN guidance. Phase one involves a systematic review to identify and assess current measurement instruments used in pouch fistula research and has been prospectively registered on PROSPERO (CRD42024505563). The second phase uses a Delphi process with international stakeholders, including patients, surgeons, gastroenterologists, radiologists and nurses, to reach consensus on the final measurement set. This will identify measurement instrument gaps and select the best available tools for each outcome. Reporting will adhere to ACCORD guidelines. This is the first international consensus to establish a core outcome measurement set for pouch fistula research. Standardized outcome measurement will enhance trial quality and facilitate stronger systematic reviews and meta-analyses. A key strength of this study is its patient-centred approach, ensuring the relevance of outcomes to the patient community, reflecting their lived experiences with pouch fistulae.