Objective: Sexual risk behaviour changes during a person's life course. Insights in sexual risk behaviour trajectories of MSM may provide starting points for the timing of HIV prevention methods. We aimed to study longitudinal trajectories of sexual risk behaviour predictive of HIV acquisition from sexual debut onwards. Design: A longitudinal study among 815 HIV-negative participants of the Amsterdam Cohort Studies (ACS) who completed extensive questionnaires about their sexual behaviour every 6 months between 2007 and 2017. Methods: A comprehensive behavioural risk score predictive of HIV seroconversion was developed. On the basis of this risk score, linear trajectories of sexual risk behaviour and MSM group membership were estimated using latent class growth mixture modelling. Associations between longitudinal trajectories and demographic and psychosocial factors were examined. Results: Three trajectories of sexual risk behaviour were identified, which were labelled Low risk (90.3% of the sample), Falling high risk (6.5%) and Rising high risk (3.3%). MSM following the Falling high risk (20.5%) and Rising high risk (25.0%) trajectories were more likely to acquire HIV during follow-up. The Falling high risk trajectory was associated with younger age at sexual debut, fewer steady partnerships and high percentages of substance use. The Rising high-risk trajectory was associated with increasing percentages of substance use over time. Conclusion: MSM follow different trajectories of changing sexual risk behaviour over time. Early identification of MSM following a trajectory of falling or rising high-risk behaviour and adequate timing of individual-based preventive interventions may reduce HIV transmission.