A case of posttraumatic syringomyelia which appeared 26 years after the injury was presented. A patient was 61 year old female, who sustained thoraco-lumbar spine injuries rendering her to paraplegic in 1954. Eleven months later she had an operation of T6-T9 and L1-L2 laminectomies and regained motor and sensory functions of the both lower extremities. She was ambulatory with crutches till 1979. In 1980, burning pain was noticed in the left scapular region, and thereafter, extended to the ulnar side of the left forearm. The pain became progressively worse and intractable. Analgesics were ineffective. Two years later muscle atrophies and weakness in the left finger intrinsic muscles appeared. Absent deep tendon reflexes in the left upper extremity, dissociated sensory loss (in the left C2-S1 and right T5-T12 dermatomes) and paraparesis were also documented. Metrizamide CT scan performed 24 hours after the intrathecal injection disclosed an intramedullary syrinx between C2 and L1 vertebral levels. No communication with the fourth ventricle was seen. A syringoperitoneal shunt with low pressure valve was placed. The pain subsided immediately after this procedure. However, no improvement in motor and sensory functions were observed. Pathophysiological mechanisms involved in post-traumatic syrinx formation and its development were discussed. We prefer hypothesis proposed by Ball and Dayan to Gardner's hydrodynamic theory regarding to development of the syrinx secondary to spinal cord injury.