Background: Pre-exposure prophylaxis (PrEP) effectively prevents HIV, but its association with sexuallytransmitted infections (STIs) has raised concerns aboutrisk compensation, potentially impacting the expansion of PrEP programmes. Aim: We examined the relationship between PrEP and the incidence of chlamydia,gonorrhoea and syphilis. Methods: In this prospective cohort study, we compared STI rates before andafter PrEP initiation among users in the capital regionof Denmark (2019–2022), calculating incidence rateratios adjusted for age and testing frequency (aIRR).To pinpoint when increases began, we plotted weeklySTI rates, adjusting the timeline to correspond withPrEP initiation. Results: The study included 1,326 PrEPusers with a median age of 35 years. The STI incidencerate per 100,000 person-years rose from 35.3 beforeto 81.2 after PrEP start, with an aIRR of 1.35 (95% CI:1.18–1.56). Notably, this increase preceded PrEP initiation by 10–20 weeks. Specific aIRR for chlamydia, gonorrhoea and syphilis were 1.23 (95% CI: 1.03–1.48),1.24 (95% CI: 1.04–1.47) and 1.15 (95% CI: 0.76–1.72),respectively. In subanalyses for anatomical sites aIRRwas 1.26 (95% CI: 1.01–1.56) for rectal chlamydia and0.66 (95% CI: 0.45–0.96) for genital gonorrhoea.Conclusion: We found a 35% increase in STI incidenceassociated with PrEP use. It started before PrEP initiation, challenging the assumption that PrEP leadsto risk compensation. Instead, the data suggest thatindividuals seek PrEP during periods of heightenedsexual risk-taking. Consequently, PrEP programmesshould include sexual health consultations, STI testing, treatment and prevention strategies to preventHIV and improve sexual health.