In this multicenter double-blind randomized study the analgesic efficacy and safety of 50 mg tramadol was compared against 50 mg pentazocine by mouth in the treatment of 160 patients with acute pain following prolapsed intervertebral disc repair. The day of surgery patients were treated with parenteral opioids. The study started the morning after surgery. A wash out period of four hours was allowed after parenteral analgesics. Pain assessment was made using a visual analogue scale (VAS) and a verbal rating scale (VRS) during a six hours observation period. Remedication with the same drug at the same dosage was allowed if pain relief was unsatisfactory. Overall analgesic activity and spontaneously reported side effects were also registered. Results showed both treatments provided equivalent effective analgesia for the six hours observation period. The global assessment of analgesia by patient and observer was not significantly different for both treatments, although less additional medication was required in the pentazocine group. Side effects were quite common in both groups, and occurred more frequently in the pentazocine group.