We describe a family with pure X-linked hereditary spastic paraplegia (HSP) and report linkage to X-chromosome DNA probes. A 6-generation pedigree (K313) with 12 affected males is presented. Eight affected males and 7 mandatory female carriers were personally examined. The disorder is characterized by delayed motor milestones and development of the typical spastic gait in adolescence. Deterioration is gradual for 20-30 years and then nonprogressive. Adults generally require crutches by age 30 and a wheelchair by age 50-60. Intelligence, upper extremity function, and vision were normal. Carrier females had a normal gait and neurologic exam. Eight X-chromosome linked DNA markers were used to genotype K313 and linkage was observed with pYNH3 (δ = 0, lod = 4.6) and DXS17 (δ = 0, lod = 4.0). These markers map to the Xq21-22 region, distinct from the Xq28 locus for complicated X-linked HSP reported by Kenwrick. These findings strongly support the clinical delineation of two distinct disease entities: pure and complicated X-linked HSP. This has important implications for genetic counseling when using DNA linked markers.