Abstract Background Surgery for aortic coarctation requires special care during anesthesia due to severe pain during the lateral thoracotomy incision, intraoperative hemodynamic instability and the need for large doses of intra- and postoperative analgesics and vasodilators. Additionally, the postoperative care of patients is very important. Aims We aimed to compare ultrasound-guided paravertebral block performed using bupivacaine alone and bupivacaine with dexamethasone in terms of the intra- and postoperative analgesic requirements and hemodynamics, postoperative complications and ICU stay. Study design This was a prospective, randomized, controlled, double-blinded study. Methods Fifty patients aged four to 12 months scheduled for aortic coarctation surgery were randomly divided into two equal groups (n = 25). Patients in group D (dexamethasone) received 0.5 mg/kg bupivacaine 0.25% mixed with 0.1 mg/kg dexamethasone diluted with isotonic saline and those in group C (control) received 0.5 mg/kg bupivacaine 0.25% diluted with isotonic saline (total volume 15 ml in each group). Intraoperative fentanyl consumption and hemodynamics (heart rate, arterial blood pressure) at baseline, 1 min after induction, at skin incision, after 30 min, after clamping, after declamping and at the end of the surgery were recorded, along with the objective pain score (OPS) immediately postoperatively and at 4 h, 8 h, 12 h and 24 h postoperatively and the time to the first request for pethidine. The intra- and postoperative vasodilator doses, time to extubation, ICU stay duration and postoperative complications were also recorded. Results The postoperative OPS was significantly lower at 12 and 24 h in group D than in group C. The time to the first request for analgesia was significantly longer in group D than in group C (3.9 ± 2.23 vs 8.6 ± 0.69). Additionally, the time to extubation was significantly shorter in group D. Conclusion The use of dexamethasone as an adjuvant in ultrasound-guided paravertebral block in paediatric patients undergoing surgery for aortic coarctation increased the duration of postoperative analgesia with a prolonged time to the first request for analgesics It was also associated with a decreased incidence of postoperative complications. Trial registration Trial registration number: NCT03074773. (Prospectively registered). The initial registration date was 9/3/2017.