Of 23 children with hereditary spastic paraplegia (HSP), spasticity was the only neurological abnormality in eight patients (pure form). Additional neurological abnormalities in the 15 with complicated HSP included cognitive impairment, pseudo-bulbar palsy, cerebellar dysfunction and polyneuropathy. 19 children presented with abnormal gait, recognised at a mean age of three years in the pure form and five years in the complicated form. These forms were distinguished at a mean age of 11 years. Early non-motor developmental delay or rapidly ascending paraparesis, with spread of spasticity to the arms and with involvement of bulbar structures, predicted development of the complicated form. The pure form was inherited in an autosomal dominant manner in five patients. The autosomal recessive form was commonly associated with additional neurological abnormalities and a more rapid rate of progression.