A 23-year-old man developed slowly progressive muscle weakness from the age of 10, followed by paresthesia and urinary disturbance. The physical examination showed bilateral muscular atrophy in the lower limbs and dissociated sensory disturbance below Th8. Although there was normal appearance of spinal X-P, MRI revealed conus medullaris at S2 involved thoraco-lumbar syringomyelia with extramedullary lipoma. After the operation for laminectomy of L5-S2 and untethering without direct surgery for syringomyelia, post-operated MRI exhibited definite shrinkage of the syrinx. It suggested that thoraco-lumbar syringomyelia in the present case was not congenital anomaly, but secondary outcome to tethered cord syndrome.