Background The analgesic efficacy of preemptive administration of caudal morphine for spine surgeries in adults is not well studied. In a double-blinded, randomized controlled trial, safety and analgesic efficacy of preemptive, single-shot caudal morphine and bupivacaine was compared with caudal bupivacaine alone in lumbosacral spine surgeries. Methods After Institutional Ethics Committee approval, 40 patients aged 18-60 yrs planned for lumbosacral spine surgery were randomized to groups of 20 patients each. After induction and prone positioning, an ultrasound-guided caudal block was performed with morphine 50 µg/kg with 20 ml 0.25% bupivacaine in the study group (LM) and only bupivacaine in the control group (LA). Postoperatively, both groups received intravenous morphine via patient-controlled analgesia (PCA) pump (No basal, 1 mg/bolus, 10 minutes lockout interval). Intraoperative fentanyl use, postoperative 24-h morphine consumption, visual analogue pain scores (VAS) and adverse effects of morphine were noted. Results Demographics and baseline data were comparable. Postoperative 24-hour morphine requirement was more in LA group (34.3 ± 10.7 mg vs 19.65 ± 11.8 mg, p=0.0001). Total intraoperative supplemental fentanyl requirement was similar (79.25 ± 67.60 µg in LA vs 54 ± 50.20 µg in LM group, p=0.28). VAS scores at 2/4/6/12-hour in group-LM were significantly less than group-LA (p=0.005, 0.002, 0.001 and 0.047) but were comparable at 18 and 24 hours (p=0.25, 0.42). Postoperative incidence of adverse effects of morphine was comparable. Conclusions Ultrasound-guided, single-shot preemptive administration of caudal morphine with bupivacaine is a safe and effective modality of analgesia for patients undergoing lumbosacral spine surgeries.