Neuropathological studies of hereditary spastic paraparesis (HSP) have described axonal loss involving corticospinal and somatosensory tracts in the spinal cord. This MRI-based study was intended to investigate in vivo diameter alterations of the spinal cord in HSP, including both pure HSP (p-HSP, n = 20) and complicated HSP (c-HSP, n = 10). Standard MRI examinations of the cervical and thoracic spinal cord in HSP patients and a control group (n = 54) were analyzed by standardized spinal cord planimetry. In HSP patients, significant atrophy of the upper spinal cord compared to controls was observed at p < 0.001 both at the cervical and at the thoracic level. Myelon diameters at both levels were also significantly reduced in the two HSP subgroups in an additional comparison with age-matched subgroups of controls each, but p-HSP and c-HSP groups themselves did not differ. Marked atrophy of the upper spinal cord seems to be associated with HSP, assumedly due to the central-distal axonopathy. However, the differences between p-HSP and c-HSP could not be visualized by structural MRI at spinal cord level.