Ganglion cysts of the spine are uncommon. They occur mostly in the dorsolateral trunk and arise with the greatest frequency in the lumbar spine. However, they are rarely symptomatic. We report a rare case of a patient with a ganglion cyst of the lower cervical spine presenting with acute Brown-Sequard syndrome. The patient had no history of trauma. Magnetic resonance imaging of the cervical spine showed a cystic lesion connecting to the synovial joint C6-7 and compressing the posterior aspect of the spinal cord. The patient underwent emergent C6-7 laminectomy with total removal of the cyst. Neurological function recovered completely 4 months after operation. Ganglion cysts should be considered in the differential diagnosis of an extradural mass of the cervical spine. Magnetic resonance imaging provides a rapid and correct diagnosis, and laminectomy with removal of the cyst results in good neurological recovery.