Hereditary spastic paraplegia(HSP) is a familial disorder which is inherited by autosomal dominant, autosomal recessive or sex linked pattern. Strumpell first described a familial case of spastic paraplegia characterized by progressive weakness and spasticity of the lower limbs. We have experienced two cases of hereditary spastic paraplegia with mental retardation and extrapyramidal symptoms with variable severity. They were sisters. Physical examination revealed increased deep tendon reflexes in all four extremities with extensor plantar reflex, and sensory losses mainly affecting joint position and vibration sensations. One case was dysmorphic. The pattern of inheritance was uncertain but considered as an autosomal recessive type. Electrodiagnostic study revealed mild slownesses in motor conduction velocities, reduced amplitude of sensory nerve action potentials and profuse abnormal spontaneous activities in distal lower extremity muscles. Somatosensory evoked potentials were not obtainable from both lower extremity stimulations, but attenuated responses without delayed latencies were obtainable from both upper extremity stimulations.