Doxycycline prophylaxis has been shown to reduce the incidence of chlamydia and syphilis infections in various studies, but researchers are worried about increasing antimicrobial resistance (AMR).1 Although not currently recommended, STI prophylaxis has been reported in high-risk men who have sex with men, with proportions ranging from 2% to 10%.2 We assessed the awareness and use of STI prophylaxis among HIV pre-exposure prophylaxis users in Belgium in a nested cross-sectional online survey in December 2021 and January 2022. Participants were recruited through social media, HIV reference centres and social/sexual networking applications. A total of 187 participants completed the survey. The median age was 46 years (IQR 38–53). The majority were born in Belgium (161/187, 86.1%) and identified themselves as male (183/187, 97.9%). Fifty-four participants (28.9%) had ever heard of STI prophylaxis, 21 (11.3%) knew someone who used it and 6 (3.2%) reported having used STI prophylaxis…