AIM: Quality of life (QoL) is a crucial and core outcome in assessing the effectiveness of treatments for cryptoglandular anal fistula. Despite its extensive impact, there is a lack of patient-centred, disease-specific QoL measurement instruments of adequate quality. The aim of this study is to develop a disease-specific measurement instrument that can accurately measure QoL for patients with cryptoglandular anal fistula. METHOD: Semi-structured qualitative patient interviews and a systematic review of current instruments were used to generate items for the draft instrument. This underwent successive rounds of cognitive interviews to refine its wording and structure. Individual item and overall scale content validity were determined by asking experts to rate the relevance of each item and those deemed irrelevant were removed. The final instrument then underwent psychometric testing and test-retest analysis to determine its sensitivity and stability. RESULTS: A total of 148 patients were involved in item generation, scale development and psychometric testing. A 22-item measurement instrument has been developed; it is scored on a scale of 0-100, where 0 indicates the worst QoL and 100 demonstrates perfect QoL. The scale demonstrates excellent internal consistency (Cronbach-α = 0.927), strong content and construct validity [correlation with Perianal Disease Activity Index = -0.713, Hospital Anxiety and Depression Anxiety (-0.659) and Depression (-0.673) subscales and Short Form-12 physical (0.609) and mental (0.589) component scales] and strong reliability and responsiveness. CONCLUSION: We have developed a cryptoglandular Anal Fistula Quality of Life scale (AF-QoL), a comprehensive, disease-specific patient reported outcome measure assessing QoL in patients with cryptoglandular anal fistula.