BackgroundLumbar spinal surgery is associated with severe postoperative pain. We examined the analgesic efficacy of bilateral lumbar ultrasound-guided erector spinae plane block (ESPB) with ropivacaine compared with local infiltration of ropivacaine.Methods Twenty-four patients undergoing elective lumbar arthrodesis were randomly divided into two groups. Control group received 0.375 % ropivacaine 40 ml through the wound, and ESPB group received preoperative bilateral ESPB with 0.375 % ropivacaine 40 ml. The primary outcome was postoperative pain intensity at rest using a Numeric Rating Scale (NRS). Secondary outcomes included difference in pain intensity between pre-intervention and defined timepoints, total amount of opioid analgesic requested by the patients at the same timepoints, the incidence of any adverse event, and the length of hospital stay (LOS) after surgery.Results After surgery we detected a NRS value of 1.9 + 1.6 in ESPB group and 6.0 + 1.7 in Control group (p<0.05). In the ESPB group we found a significant decrease (from 6.3 ± 1.6 to 1.9 ± 1.7) of NRS score after surgery compared to pre-surgery values. About the opioid consumption we found a total sufentanil tablets consumption of 17 ± 9 and 10 ± 2 at 48h for Control group and ESPB group, respectively. Concerning LOS all patients in the Control group and 9 of the ESPB group were discharged after 72 hours; 3 patients in the ESPB group left the ward after 48 hours. Conclusion Bilateral ultrasound-guided ESPB offers improved postoperative analgesia compared with local infiltration in patients undergoing lumbar spinal surgery.Trial Registration Number on Clinicaltrial.gov: NCT04123106