Study Design. Case-control study. Objective. Investigate the association between lumbar spine magnetic resonance imaging (MRI) findings and 5-year trajectories of low back pain (LBP) in young Australian adults. Summary of Background Data. The association between lumbar spine imaging findings and LBP remains unclear due to important limitations of previous research, such as a lack of clearly defined LBP phenotypes and inadequate controlling for age, which may substantially affect the association. Methods. Seventy-eight ‘‘case’’ participants with a previously identified ‘‘consistent high disabling LBP’’ trajectory from age 17 to 22 years and 78 ‘‘control’’ participants from a trajectory with consistently low LBP over the same time period, matched for sex, body mass index, physical activity levels, and work physical demands, were identified from Gen2 Raine Study participants. At age 27, participants underwent a standardized lumbar MRI scan, from which 14 specific MRI phenotypes were identified. Primary analyses used unconditional logistic regression, adjusting for covariates used in the matching process, to investigate the relationship between presence of each imaging finding and being a case or control. Secondary analyses explored those relationships based on the number of spinal levels with each MRI finding. Results. The odds for being a case compared with a control were higher in those with disc degeneration (Pfirrmann grade ≥ 3; OR = 3.21, 95% CI: 1.60 – 6.44; P = 0.001) or those with a herniation (OR = 1.90, 95% CI: 0.96 – 3.74; P – 0.065). We also found that the association became substantially stronger when either disc degeneration or herniation was present at two or more spinal levels (OR = 5.56, 95% CI: 1.97 – 15.70; P = 0.001, and OR = 5.85, 95% CI: 1.54 – 22.25; P = 0.009, respectively). The other investigated MRI findings were not associated with greater odds of being a case. Conclusion. Lumbar disc degeneration and herniation may be important contributors to disabling LBP in young adults. Further investigation of their potential prognostic and causal roles is indicated.