A 71-year-old man with ankylosing spondylitis and an unstable fracture of the 6th and 7th cervical vertebrae was managed with a halo vest. Eight weeks following application the halo had shifted because of a loose pin. The patient’s only complaint at the time was a headache but this was followed two days later by a seizure. An MR scan of the brain showed a swollen cortex under the right dorsal pin as a result of a perforation of the internal lamina by the pin. The halo was removed and anti-epileptic medication commenced. The patient had no further seizures.