We describe the accidental injection of local anesthetics containing steroid into the subdural space during an attempted lumbar epidural injection for intractable radiculopathy in a patient with failed back surgery syndrome. A 24-year-old man complained of severe radiating pain to left lower extremity and showed a walking disturbance and severe lumbar scoliosis. The MRI finding was a left paramedian recurred disc herniation on L4-5 in a laminectomy state. Several therapeutic modalities such as epidural steroid injection, transforaminal injection, L2 root block, medication, and exercise therapy, etc failed. Initially, during epidural block at L4-5 under fluoroscopic guidance, a railroad track appearance appeared on epidurogram suggesting the presence of a subdural space. A second epidural block was tried at L5-S1. Following confirmation of epidural space upon epidurogram, 6 ml of 0.5% lidocaine including triamcinolone 40 mg was injected. The patient showed signs of the subdural injection including an unexpectedly high sensory block (T2) and a motor weakness of both lower extremities. Following this event, the severe radiculopathy and lumbar scoliosis were improved. Therefore, we conclude that subdural injection of steroid could be helpful in intractable radiculopathy, especially in the failed back surgery syndrome. However, it must be used cautiously with careful patient selection.