Study Design. Cross-sectional, community-based studyObjective. To investigate the relationships between obesity, disc height and low back pain in the lumbosacral spine.Summary of Background Data. Although obesity is a recognised risk factor for low back pain, our understanding of the mechanisms for this is limited. The evidence for an association between obesity and spinal structural changes is also conflicting.Methods. 72 participants from a community-based study of musculoskeletal health underwent Magnetic Resonance Imaging from the T12 vertebral body to the sacrum. Disc height was measured from L1/2 to L5/S1. Body mass index was measured and low back pain in the previous 2 weeks was assessed.Results. The mean and total lumbar disc heights were reduced in obese compared to non-obese individuals (mean height(SE):1.04(0.03)cm vs 1.14(0.02)cm,p = 0.01; total height(SE):4.16(0.11)cm vs 4.57(0.10)cm,p = 0.01), after adjusting for age, gender and height. While obesity was associated with reduced disc heights at the L1/2 and L3/4 levels, there were no significant relationship at the lumbosacral junction (mean difference (95 CI):0.10(-0.14, 0.16)cm,p = 0.89). Both mean and total lumbar disc heights were negatively associated with recent pain after adjusting for age, gender and height (mean height: mean difference (95 CI):0.09(0.02, 0.17)cm,p = 0.02; total height: mean difference (95 CI): 0.37(0.07,0.66)cm,p = 0.02). However, these relationships were no longer significant when we also adjusted for weight (mean height; mean difference (95 CI):0.07(-0.009,0.15)cm,p = 0.08; total height: mean difference (95 CI):0.28(-0.04, 0.60)cm,p = 0.08). There were no significant relationships between disc height and recent pain at the lumbosacral junction.Conclusions. Obesity was associated with reduced disc height in the lumbar spine, but not at the lumbosacral junction, suggesting these joints may have different risk factors. There was also evidence for an inter-relationship between obesity, lumbar disc height and recent pain, suggesting that structural changes have a role in back pain and may in part explain the association between obesity and back pain.