A case is presented of extracranial duplication of the vertebral artery in a patient who had spinal cord symptoms for 26 years. Vertebral angiograms and computed tomography with metrizamide enhancement demonstrated a bypass artery of the duplication compresing the upper cervical spinal cord intradurally at the level of the atlas; this finding was verified at operation. The symptomatology and clinical significance of this rare case are discussed.