To identify developmental trajectories of drinking between the ages of 18 and 26 years and to identify variables, amenable to policy influence, which predict these trajectories. Longitudinal data were analysed using latent class mixture modelling. Participants were interviewed in a central location. Provincial city birth cohort, cross-national studies suggest findings are generalizable to other similar market economies. The frequency of drinking over the past year and the typical quantity consumed per drinking occasion were computed from five location-specific questions. Measures used to predict membership of trajectory groups were ease of access to alcohol, drinking on licensed premises, response to alcohol advertising, educational achievement, parental consumption, age of onset of regular drinking and living arrangements. Three trajectories of quantities consumed showed reduced consumption after age 21 but one trajectory showed marked increases. Three trajectories of frequency of drinking increased or remained stable over time. Access to licensed premises at age 18 had the most significant impact on membership of the trajectory groups and educational achievement had a significant impact on membership of the heavier quantity trajectory groups. Parental alcohol consumption, access to alcohol at 15 years, liking for alcohol advertising, living arrangement and age of onset of regular drinking also influenced trajectory membership. Quantity and frequency of drinking in adolescence and early adulthood had different trajectories. Membership of heavier drinking groups was affected by environmental influences which are subject to policy change, particularly that of earlier access to licensed premises. In a small group high-quantity consumption did not decrease at age 26.