BACKGROUND: Gay, bisexual and other men who have sex with men (gbMSM) who attend STI clinics represent an easily accessible population for promoting HIV prevention interventions. We examined characteristics of gbMSM STI clinic attendees to identify those who could most benefit from pre-exposure prophylaxis (PrEP). SETTING: GbMSM STI clinic attendees in British Columbia (BC), Canada. METHODS: A clinical electronic charting system of STI clinics in BC was used to identify gbMSM from 2004 to 2017. Incident HIV cases were defined as testers who had at least one HIV-negative test and a subsequent HIV-positive test. Seroconversion rates were calculated by risk factor variables and by year. Cox proportional hazards regression was used to identify independent predictors of HIV seroconversion. RESULTS: There were 9,038 gbMSM included, of whom 257 HIV seroconverted over the study period and 8,781 remained negative HIV testers, contributing 650.8 and 29,591.0 person-years to the analysis, respectively. The overall rate of seroconversion was 0.85 per 100 person-years (95% CI: 0.75-0.96). Incidence rates were higher among patients reporting >5 partners in the previous six months, inconsistent condom use, or having a partner living with HIV and who had a previous or concurrent diagnosis of rectal gonorrhea or rectal chlamydia. gbMSM presenting with two STIs such as rectal gonorrhea and syphilis (3.59/100 person-years [95%CI: 2.33-5.22]) or rectal chlamydia and syphilis (3.01/100 person-years [95%CI: 2.00-4.29]) had the highest incidence rates. CONCLUSION: gbMSM with preceding or concurrent rectal STI diagnoses or syphilis had higher rates of HIV seroconversion. The data support the inclusion of specific STI diagnoses as an indication for PrEP.