OBJECTIVE: To delineate fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of compressed nerve roots in patients with lumbar disc herniation by diffusion tensor imaging and fiber bundle tracing and investigate the relationship between FA and ADC values and Swiss Spinal Stenosis Questionnaire and visual analog scale scores. METHODS: Twenty patients with lumbar disc herniation and 20 age-and sex-matched healthy volunteers were assessed using the Swiss Spinal Stenosis Questionnaire and visual analog scale. All subjects underwent conventional sagittal T1-weighted and T2-weighted magnetic resonance imaging, axial T2-weighted imaging, and diffusion tensor imaging and fiber tractography. RESULTS: In 20 patients with lumbar disc herniation, there were 31 nerve roots involved (9/31 L4, 15/31 L5, and 7/31 S1). Mean Swiss Spinal Stenosis Questionnaire scores of patients were 53.55% +/- 11.91%, and mean visual analog scale scores were 5.96 +/- 1.64. FA values of lumbar nerve roots were 0.332 +/- 0.014 in healthy volunteers. FA values of compressed lumbar nerve roots were 0.251 +/- 0.022, significantly lower than FA values of contralateral non-compressed nerve roots and lumbar nerve roots of healthy volunteers. ADC values of lumbar nerve roots were 1.763 +/- 0.075 in healthy volunteers. ADC values of compressed lumbar nerve roots were 2.090 +/- 0.078, significantly higher than ADC values of contralateral noncompressed nerve roots and lumbar nerve roots of healthy volunteers. CONCLUSIONS: Fiber tractography is capable of delineating microstructural changes of lumbosacral nerve roots, and radiculopathy in lumbar disc herniation is associated with significant changes in FA and ADC values.