The pattern of fibre degeneration in the lateral corticospinal tract (LCST) was studied in a case of Friedreich's ataxia (FA). There was preferential involvement of the lateral area of the LCST in the cervical spinal cord. More caudally, the degeneration involved the entire area of the LCST and did not reveal a medial to lateral gradient of involvement. We suggest that this distinctive pattern of tract degeneration is a consequence of the somatotopic organization of the LCST, with the dying-back degeneration preferentially affecting those LCST fibers that extend to the lumbo-sacral spinal cord. This pattern of tract degeneration may be a useful morphological marker of dying-back degeneration in corticospinal tracts.