BACKGROUND: The combination of a local anesthetic and an opioid has been shown to produce effective epidural labor analgesia. It was reported that the combination of intrathecal opioid and bupivacaine could produce labor analgesia with longer duration and less side effects. This study was done to evaluate the effect of intrathecal bupivacaine mixed with sufentanil for labor analgesia. METHODS: Eighty women requesting labor analgesia were randomly assigned to receive intrathecal 10 mcg of sufentanil (S group, n = 40) or 2.5 mg of bupivacaine plus 10 microgram of sufentanil (SB group, n = 40) diluted in a total volume of 2.2 ml with normal saline. The analgesia was performed using combined spinal-epidural technique in the lateral position. Visual analogue scales (VAS) for pain, sensory changes to cold, duration of analgesia, motor block, hypotension, fetal heart rate, pruritus, and other side effects were assessed for 30 minutes after intrathecal drug injection. RESULTS: There were no significant differences in the VAS pain scores and sensory levels at 5 minutes after intrathecal drug injection between groups. However, VAS pain scores were significantly lower and sensory levels higher in the SB group at 15 minutes and 30 minutes after intrathecal drug injection. The duration of analgesia provided by intrathecal sufentanil (n = 31) was 103.4 41.1 min, by intrathecal sufentanil plus bupivacaine (n = 29) 113.0 32.1 min (P = 0.30). Motor block assessed by a modified Bromage scale was significantly frequent in the SB group (P< 0.001). Not only adverse effects such as hypotension, fetal bradycardia, pruritus, and nausea, but also satisfaction scores were similar in both groups. CONCLUSIONS: The addition of bupivacaine to intrathecal sufentanil produced more frequent motor block and extensive sensory block, but better analgesia. However, duration of analgesia, side effects and satisfaction score did not change.