Objectives: To (i) quantify relationships between LBP symptoms, physical activity, and psychosocial characteristics in young adults and (ii) identify sub-classes of young adults with distinct pain trajectories. Design: Prospective cohort study with 12 months follow-up Methods: 120 adults (age 20.8±2.6 years, 99 women) participated. Participants completed a baseline survey that measured anxiety, depression, fear avoidance, quality of life, and history and impact of any LBP. Participants completed follow up surveys every 3 months for one year. Sub-classes based on pain trajectories over time were identified using latent class analysis and predictors of class membership at baseline were assessed. Results: Individuals with LBP at baseline had lower physical quality of life scores than back-healthy participants (P = 0.01). Sub-class 1 (25% of individuals with LBP) had persistent moderate/high intensity of pain over the 1-year study period. Sub-class 2 (75%) had significantly improving pain over the 1-year study period. Higher fear avoidance (physical subscale) and pain interference at baseline were associated with greater odds of membership of sub-class 1 (odds ratios 1.2 (95% CI 1.01– 0.1.32) and 1.4, (95% CI 1.15 – 1.64) respectively). Conclusion: Most young adults with LBP had symptoms that improved over time. Levels of fear avoidance and pain interference may help to identify individuals at risk of persistent pain early in the lifespan.