['Neostigmine extends the duration of analgesia produced by caudal bupivacaine in children.', 'To study the effect of different doses of caudal neostigmine on the duration of postoperative analgesia.', 'A randomized, double-blind study was conducted in 120 boys aged 1-12 years undergoing urethroplasty under combined general and caudal anesthesia.', 'Children were administered 1.875 mg/kg bupivacaine alone (Group B) or with 2, 3 or 4 microg/kg of neostigmine (groups BN 2, BN 3 or BN 4 respectively) as caudal drug (0.75 ml/kg). Children with a pain score of 4 or more (OPS and NRS) postoperatively were administered rescue analgesic. Time to first analgesic and the number of analgesic doses administered in the 24h were recorded.', 'Parametric data were analyzed using ANOVA. Kaplan-Meier survival curves for the time to first analgesic administration were plotted and compared using log rank analysis. Chi-square test was used to analyze the incidence data.', 'The median [IQR] time to first analgesic in Group B (540 [240-1441] min) was similar to that in Groups BN 2 (450 [240-720]), BN 3 (600 [360-1020]) and BN 4 (990 [420-1441]). Significantly more patients in Groups B (9 [34.6%]) and BN 4 (13 [44.8%]) required no supplemental analgesic for 24h than those in Groups BN 2 and BN 3 (4 [13.8%] and 4 [13.3%]). The number of analgesic doses required in 24h in the four groups was similar.'] Does neostigmine prolong the duration of analgesia produced by caudal bupivacaine in children undergoing urethroplasty?