Signs and Symptoms consistent with the irritation of the cauda equina developed during epidural morphine therapy for the relief of pain from osteosarcoma in a 10-year-old female patient. This was considered to be due to a subarachnoid diffusion of the epidurally administrated morphine through the dural opening formed by a previous inadvertent dural puncture. The subarachnoid diffusion of the drug was confirmed by fluoroscopy following injection of the contrast media through the indwelling epidural catheter. The chemical inflammation of the cauda equina might be due to substances formed by chemical reactions with a certain preservative vehicle rather than the morphine itself. Spinal steroid therapy may be effective for the suppression of a chemical inflammatory reaction.