OBJECTIVES To examine patterns of long-term pre-exposure prophylaxis (PrEP) adherence and its association with HIV seroconversion in NSW, Australia. DESIGN Population-based HIV PrEP implementation study. METHODS Expanded PrEP Implementation in Communities in New South Wales was an open-label study of daily oral PrEP which recruited participants from March 2016 to April 2018. Adherence was measured using dispensing records. PrEP discontinuation was defined as an at least 120-day period without PrEP coverage. Long-term adherence patterns were identified using group-based trajectory modelling. RESULTS Participants dispensed at least once (n = 9586) were almost all male (98.5%), identified as gay (91.3%), with a median age of 34 years (range: 18-86). Of the 6460 (67.4%) participants who had at least 9 months of follow-up since first dispensing, 1942 (30.1%) discontinued. Among these, 292 (15.0%) restarted later. Four distinct groups were identified ['Steep decline' in adherence (15.8%), 'Steady decline' (11.6%), 'Good adherence' (37.4%), and 'Excellent adherence' (35.2%)]. Older (P