ObjectiveThe hepatitis C virus (HCV) epidemic among gay, bisexual and other men who have sex with men (GBMSM) is associated with sexual and drug-related behaviours. To stem the tide of HCV infection in GBMSM, regular testing leading to early diagnosis and treatment as prevention is vital. This study aimed to evaluate the success of current HCV testing guidelines from the perspective of GBMSM in four Celtic nations.MethodsSubpopulation analysis of data from the 2020 cross-sectional online SMMASH3 (social media, men who have sex with men, sexual and holistic health) survey was undertaken to examine HCV testing experiences and sexual behaviours among sexually active GBMSM (n=1886) stratified across three groups: HIV-diagnosed GBMSM (n=124); HIV-negative GBMSM using pre-exposure prophylaxis (PrEP) (n=365); and HIV-negative/untested GBMSMnotusing PrEP (n=1397).ResultsSexual behaviours associated with HCV acquisition were reported by the majority of HIV-diagnosed (76.6%, n=95) and PrEP-using (93.2%, n=340) GBMSM. Reassuringly, recent testing for HCV in these groups was common, with 79.8% (n=99) and 80.5% (n=294) self-reporting HCV screening within the preceding year, respectively, mostly within sexual health settings. While 54.5% (n=762) of HIV-negative/untested GBMSM not using PrEP reported sexual behaviours associated with HCV, 52.0% had not been screened for HCV in the last year, despite almost half (48.0%, n=190) of unscreened men being in contact with sexual health services in the same period.ConclusionsSexual behaviours associated with HCV acquisition among HIV-diagnosed and PrEP-using GBMSM are common but complemented by regular HCV testing within sexual health services. Current testing guidelines for these groups appear to be effective and generally well observed. However, behaviour-based HCV testing for HIV-negative/untested GBMSMnotusing PrEP appears less effective and may undermine efforts to achieve HCV elimination. Accordingly, we need to increase HCV testing for these men in clinical settings and explore ways to screen those who are not in touch with sexual health services.