The addition of opioids to local anesthetics improves the analgesic potency of spinal analgesia. The purpose of this study was to evaluate the efficacy and safety of intrathecal fentanyl 15 microg when added to lidocaine 80 mg in patients undergoing Cesarean section under spinal anesthesia. Forty healthy parturients scheduled for elective Cesarean section using 80 mg of 5% lidocaine were randomly allocated to additionally 0.9% receive intrathecal fentanyl 15 or saline, as control. Characteristics of spinal block, intraoperative quality of spinal anesthesia, side effects, time of first feeling of pain (complete analgesia) and time to first request of analgesics (effective analgesia) were assessed. Duration of sensory block was prolonged in the fentanyl group (p < 0.05). The quality of intraoperative analgesia was also better. Incidence of side effects did not differ between groups. Duration of complete analgesia (140.2 +/- 29.06 minutes vs 77.90 +/- 20.21 minutes: P < 0.001) and effective analgesia (195.50 +/- 34.06 minutes vs 98.05 +/- 23.48 minutes: P < 0.001) were prolonged in fentanyl group. Adding fentanyl 15 microg to lidocaine 80 mg for spinal anesthesia for Cesarean section, improves the quality of intraoperative analgesia and increases the duration of analgesia in the early postoperative period without increasing maternal or neonatal side effects.