PrELUDE study evaluated daily pre-exposure prophylaxis (PrEP) in high-risk individuals in Australia. This open-label, single-arm study tested participants for HIV/STI and collected behavioural information three-monthly. We report trends over 18 months in medication adherence, side-effects, HIV/STI incidence and behaviour. 320 gay/bisexual men (GBM), 4 women and 3 transgender participants, followed on average 461 days, reported taking seven pills/week on 1,591 (88.5%) occasions and 4-6 pills/week on 153 (8.5%) occasions. No HIV infections were observed. STI incidence was high and stable, while gonorrhoea infections declined from 100.0 to 25.8/100 person-years between 6 and 15 months (p < 0.001). The number of HIV-positive and unknown-status sex partners, and condomless anal intercourse, significantly increased. In this high-risk cohort of mainly GBM, increases in risk behaviours and high STI incidence were not accompanied by HIV infections due to high adherence to daily PrEP. The study informed policy and further PrEP implementation among Australian GBM.