We describe the case of a 30-year-old patient who was referred for lumbar epidural corticosteroid injection due to right L5 radiculopathy. Two months earlier, MRI demonstrated a right large paracentral L4-L5 disk extrusion causing disabling L5 radiculopathy. The L4-L5 level was selected for interlaminar injection, using fluoroscopic guidance. During injection, the patient developed severe pain in both lower extremities. Thus, the procedure was immediately terminated. Paraplegia occurred within several minutes. Urgent lumbar spine CT and MRI demonstrated contrast material in a massive extruded disk fragment and substantial increase in size of the disk extrusion compared to pre-injection MRI. Emergency surgery was performed for lumbar decompression and discectomy. Although rare, serious neurological complication can result from inadvertent intradiscal injection of contrast material during lumbar epidural injection. This case illustrates the importance of recognizing the possibility of dynamic change in the size of an extruded disk fragment when the MRI precedes injection by a substantial time interval. LEVEL OF EVIDENCE: IV, Case Series.