To develop a cryptoglandular Anal Fistula Core Outcome Set: a minimum set of outcomes that should be measured in all studies of cryptoglandular anal fistula treatment. Variability in the outcomes that are reported in studies of cryptoglandular anal fistula treatment hampers systematic evidence synthesis to identify the best treatment. This study followed guidance from the Core Outcome Measures in Effectiveness Trials initiative and consisted of three stages: (1) generation of candidate outcomes through systematic review of the literature and qualitative patient interviews; (2) prioritization of outcomes by key stakeholders, including patients, surgeons, gastroenterologists, and radiologists in an online Delphi consensus process; and (3) determination of the final Core Outcome Set (COS) in a consensus meeting attended by patients and clinicians. Sixty-four outcomes were presented in the first Delphi survey round. A total of 191 participants from over 30 countries ranked these outcomes according to their importance in defining treatment success (57.6% surgeons and gastroenterologists, 8.9% radiologists, and 33.5% patients). After two rounds, 53 outcomes were identified as important and discussed in the consensus meeting attended by 10 patients and 12 clinicians. A final 10 outcomes were voted into the COS: clinical fistula healing, radiological healing, recurrence, development of additional fistulas, fistula symptoms, incontinence, psychological impact of treatment, complications and reinterventions, patient satisfaction, and quality of life. The final COS represents an international, multidisciplinary, patient-centered attempt to establish consistency in fistula research, with a substantial focus on patient priorities for treatment.