Hoornenborg E, et al. - Changes in sexual behaviour between baseline and 6 months after pre-exposure prophylaxis (PrEP) initiation among MSM and transgender women (TGW) were examined in this prospective, open-label demonstration study performed at a large sexually transmitted infection (STI) clinic in Amsterdam, the Netherlands. Findings revealed an increase in insertive and receptive condomless anal sex acts (CASa) with casual partners over the first 6 months after initiation of PrEP. Older age, prior engagement in chemsex, recent use of postexposure prophylaxis and choosing a daily PrEP regimen at baseline were identified to be correlated with an increase in receptive condomless anal sex acts (rCASa) with casual partners.