Hereditary spastic paraplegia refers to a group of clinically similar disorders whose primary feature is insidiously progressive lower extremity weakness and spasticity. Hereditary spastic paraplegia is genetically diverse: loci for autosomal recessive (chromosome 8p), autosomal dominant (chromosome 2p, 14q, and 15q), and x-linked hereditary spastic paraplegia have been identified. The existence of hereditary spastic paraplegia families for whom the disorder is unlinked to these loci indicates the existence of additional, as yet undiscovered, hereditary spastic paraplegia loci. Hereditary spastic paraplegia exhibits axonal degeneration that is maximal at the terminal portions of the longest central nervous system axons. Efforts to positionally clone the hereditary spastic paraplegia gene are in progress.