Background: Previous anatomic studies have shown the conus medullaris to terminate between T12 and L1 vertebral levels in adults with normal spinal anatomy. Prior anatomic and radiographic studies of conus position with flexion and extension of the spine have had conflicting results. We performed a cadaveric study with direct visualization of the conus during flexion and extension to further study this question and potentially determine if flexion and extension of the spine during magnetic resonance imaging may prove to be a diagnostic tool in such pathologies as occult tethered cord syndrome. Materials and methods: We performed T12 to L3 laminectomies in five fresh adult cadavers and exposed the conus and cauda equina. Cadavers were fully flexed at the waist and neck and the conus position observed. Results: In all specimens, the conus terminated between T12 and L1 in the prone position. During flexion, the conus position remained stable with no ascent. However, flexion produced stretching and medial displacement of the cauda equina. Conclusions: Flexion of the spine does not cause the conus medullaris to change position in fresh human cadavers; however, flexion does cause the cauda equina to stretch and displace medially over the conus. Therefore, it is unlikely that the conus would change position during spine flexion during imaging or procedures such as lumbar puncture. © Springer-Verlag 2008.