<p>Insufficient lung expansion due to inadequate pain management and opioid consumption is one of the most important factor for perioperative atelectasis and and the use of ultrasound in the diagnosis of atelectasis has been quite common in recent years. The effectiveness of posterior quadratus lumborum block (QLB) in postoperative analgesia after open surgery is well established. The present study aimed to investigate the effects of posterior QLB on perioperative atelectasis in pediatric surgeries. Sixty patients who underwent elective inguinal hernia repair and orchipexy surgery under general anesthesia were included in the study. The patients were divided into 2 groups: Control (<i>n</i> = 30) and QLB, (<i>n</i> = 30). Posterior quadratus lumborum block was administered to the QLB group. Incidence of atelectasis and modified lung ultrasound (LUS) scores were recorded before induction (T1), at the end of surgery (T2), and before leaving the recovery unit (1&#xa0;h after extubation) (T3). Pain was evaluated with Face, Legs, Activity, Cry, Consolability (FLACC) scores in the postoperative period. The analgesics administered in the recovery unit and ward were recorded. A significant difference was observed in the incidence of atelectasis and total LUS scores between groups at T2 and T3. Both outcomes were higher in the control group. A significant difference was observed between the groups in terms of FLACC scores at 0, 2, and 6&#xa0;h postoperatively. In all three time periods, the scores in the QLB group were lower. A significant difference was observed between the groups in terms of rescue analgesic usage in the recover room and during ward follow-up. Analgesia requirement was higher in the Control group. Ultrasound-guided posterior QLB in pediatric patients undergoing inguinal hernia repair and orchiopexy surgery decreases the incidence of atelectasis and total LUS scores by reducing pain scores and the amount of opioids required. Trial registration: NCT04830280 registered 2021/03–11.</p>