An 88-year-old woman with an undiagnosed chronic subdural haematoma underwent emergency repair of a femora hernia under spinal anaesthesia. The patient complained of headache postoperatively, and a subsequent computed tomography brain scan showed an acute-on-chronic subdural haematoma, with midline shift and impending coning. The patient recovered completely after surgical decompression. The difficulty in diagnosing chronic subdural haematoma in the elderly patient with no history of trauma is discussed, along with the differential diagnosis of headache following spinal anaesthetic in this age-group.