This study aimed to identify body mass index (BMI) trajectories from childhood and their relationships with depression, anxiety, and stress symptoms in young adulthood. A total of 687 children aged 4-18 years were recruited from the Tehran Lipid and Glucose Study. Throughout 18 years of follow-up, BMI was measured every 3 years for a maximum of 6 data points. Participants completed the depression, anxiety, and stress scale in their young adulthood (aged 22-36). The group-based trajectory modelling was applied to identify BMI patterns. The logistic regression model was used to assess the association between BMI trajectories and depression, anxiety, and stress symptoms in adulthood. Two BMI trajectories were identified from childhood to young adulthood: healthy weight (HW = 69.6%) and persistent increasing overweight/obesity (PIO = 30.4%). After adjusting for potential confounders, compared with the HW group, men in the PIO group were more likely to experience higher stress levels (OR: 1.62, 95% CI: 0.99-2.63; p = 0.05). No significant association was observed between the PIO trajectory and depression and anxiety among both sexes and stress symptoms in females. Our results highlight that developing overweight and obesity from childhood may be related to increased stress in males.