Background A limited number of studies have demonstrated that there may be distinct developmental trajectories of obesity during childhood. Objective To identify distinct trajectories of body mass index (BMI) in a large sample of Australian children. Methods Participants included 4601 children aged 45 years at baseline, who were followed up at ages 67 years, 89 years and 1011 years. Height and weight were measured at each of these time points, and used to calculate BMI. Growth Mixture Modelling was used to identify the presence of distinct BMI trajectories. Results Four distinct trajectories were identified (i) High Risk Overweight; (ii) Early Onset Overweight; (iii) Later Onset Overweight and (iv) Healthy Weight. Further analyses indicated that factors such as parental overweight, parent education, parent smoking and child birth weight were significant predictors of these trajectories. Conclusion These findings indicate that different patterns of BMI development exist in children, which may require tailored interventions.