The patient had lower lumbar arachnoiditis as part of a failed back surgery syndrome. Two years after discectomy, she still suffered from left lumbosciatic pain despite various invasive treatments. Psychologic impairment could be excluded. Finally, intrathecal morphine was infused at the D12 level. Small amounts of morphine (500–750 mg daily) introduced intolerable vomiting, which could not be prevented by antiemetics, so intrathecal sufentanil was started. A daily dose of 25 mg of sufentanil diluted in 1.5 ml of saline evoked hyperalgesia in the lower part of the body. Increasing the dose to 50 mg daily could only be supported for 3 h. Sufentanil was stopped and saline started, after which the evoked hyperalgesia disappeared. It is concluded that relatively high doses of sufentanil may induce hyperalgesia in patients with arachnoiditis and neuropathic pain.