Syringomyelia is an uncommon disease that is caused most often by type I Chiari malformation, which develops in the hindbrain, and less frequently by other factors which are not limited to the hindbrain, including trauma, infection, or scoliosis. Idiopathic syringomyelia is rare. We present in this article a patient with idiopathic syringomyelia characterized by hypoesthesia and progressive weakness in the left lower limb. Decompression was attempted by means of laminectomy and a syringoarachnoid shunt. Motor, sensory, and bladder functions were monitored by the change in Japanese Orthopedic Association scores, which increased from 10 points preoperatively to 14 points 30 days postoperatively. This case demonstrates the effectiveness of surgical decompression in a patient with remarkable neurological deficit.