Mutations in the SPG3A gene (atlastin protein) cause approximately 10% of autosomal-dominant hereditary spastic paraplegia. Most patients with an SPG3A mutation present with a pure phenotype and early-onset disease, although complicated forms with peripheral neuropathy are also reported. We report a new heterozygous S398F mutation in exon 12 of the SPG3A gene causing a very early-onset spastic paraplegia in association with motor axonal neuropathy in a 4-year-old girl resembling diplegic cerebral palsy.