Objective: To report on an unusual knife stab injury of the thoracic spine, causing an acute subdural haematoma (SDH) and paraparesis. Setting: Department of Surgical Neurology, Ward 20, The Royal Infirmary of Edinburgh. Case report: The weapon was a knife, which traversed the mid-thoracic spinal region, causing an incomplete spinal cord lesion, which was demonstrated by myelography to be due to an SDH. The haematoma was removed at operation. There was a full neurological recovery. Conclusion: There was no bony injury. The likely cause for the development of the SDH was believed to be due to the sudden impingement on the spine by the weapon, rupturing small subdural veins.Spinal Cord (2005) 43, 678-679.