Background and objective: The quality of spinal anaesthesia, often used for Caesarean section, can be improved by adding an opioid to the local anaesthetic. This study compared the quality of anaesthesia, postoperative analgesia, and adverse effects on mother and neonate when either sufentanil 5 mu g or morphine 0.2 mg was added to intrathecal hyperbaric bupivacaine for Caesarean section. Methods: This prospective, randomized and double-blind study encompassed 54 females undergoing Caesarean section. Spinal anaesthesia was obtained with 2 mL of 0.5% bupivacaine supplemented with either 0.2 mg morphine or 5 mu g sufentanil. Characteristics of spinal block, intraoperative analgesia, maternal and neonatal side-effects and the time to first request for analgesics were assessed. Results: There were no differences in the onset time of sensory block, time to sensory block to T-10, time to highest sensory block, highest sensory block level, time to regression of sensory block to T-10 level and time to resolution of motor blockade. Perioperative haemodynamic parameters, neonatal Apgar scores, neurological and adaptive capacity scores, umbilical blood gas values, sedation scores, nausea-vomiting and pruritus incidences were similar in both groups. The time to the First request for an analgesic was significantly longer (19.5 +/- 4.7 h vs. 6.3 +/- 5.2 h) in patients given morphine (P < 0.05). Conclusions: The addition of 5 mu g sufentanil or 0.2 mg morphine to hyperbaric bupivacaine for Caesarean section both provided safe and effective anaesthesia. Morphine increased the duration of postoperative analgesia compared with sufentanil without increasing maternal or neonatal side-effects.