STUDY DESIGN: Cross-sectional cohort study of a general population. OBJECTIVE: To investigate "abnormal" lumbar spine magnetic resonance imaging (MRI) findings, and their prevalence and associations with low back pain (LBP). SUMMARY OF BACKGROUND DATA: The clinical relevance of various "abnormal" findings in the lumbar spine is unclear. Distinguishing between inevitable age-related findings and degenerative findings with deleterious consequences is a challenge. METHODS: Lumbar spine MRI was obtained in 412, 40-year-old individuals. Predefined "abnormal" MRI findings were interpreted without any knowledge of patient symptoms. Associations between MRI abnormalities and LBP were calculated using odds ratios. The "overall picture" of each MRI finding was established on the basis of the frequencies, diagnostic values, and the strength and consistency of associations. RESULTS: Most "abnormal" MRI findings were found at the lowest lumbar levels. Irregular nucleus shape and reduced disc height were common (>50% of individuals). Relatively common (25% to 50%) were hypointense disc signal, anular tears, high intensity zones, disc protrusions, endplate changes, zygapophyseal joint degeneration, asymmetry, and foraminal stenosis. Nerve root compromise, Modic changes, central spinal stenosis, and anterolisthesis/retrolisthesis were rare (<25%). Most strongly associated with LBP were Modic changes and anterolisthesis (odds ratios >4). Significantly positive associations with all LBP variables were seen for hypointense disc signals, reduced disc height, and Modic changes. All disc "abnormalities" except protrusion were moderately associated with LBP during the past year. CONCLUSION: Most degenerative disc "abnormalities" were moderately associated with LBP. The strongest associations were noted for Modic changes and anterolisthesis. Further studies are needed to define clinical relevance.