© 2021, Springer Medizin Verlag GmbH, ein Teil von Springer Nature.Background: The effects and analgesic adequacy of intrathecal morphine (ITM) administration have been studied less frequently than other regional analgesia techniques in pediatric surgical procedures. Objective: To evaluate the efficacy and adverse event rate of 5 µg/kg ITM administration for postoperative analgesia according to age group. Methods: We retrospectively evaluated the medical records of patients who underwent major pediatric surgery and were administered ITM for postoperative analgesia. Patients were divided into three age groups: ≤ 5 years (group I), 5.1–13 years (group II) and > 13 years (group III). All patients received ITM 5 µg/kg (max 300 μg) through the L4–5 or L5–S1 interspace. Postoperative pain (modified pediatric objective pain score > 4), need for rescue analgesics, sleep interruption due to pain, sedation (Ramsay sedation scale score > 3), opioid-related postoperative adverse events (at 0, 4, 8, 12, and 24 h after intervention), hemodynamic data and nurse satisfaction with the analgesic method were compared between groups. Results: The analysis included 100 children (47 girls, 9 ± 5.4 years). Groups were similar regarding postoperative rescue analgesia consumption and sleep interruption (p = 0.238, p = 0.958), 96% of the children did not require rescue analgesia, and sleep interruption was not observed in 97%. Postoperative adverse events were pruritus in 14 and nausea/vomiting in 9 patients (p = 0.052). Overall, nurses were satisfied or very satisfied in 99% of the cases. Conclusion: Administration of 5 µg/kg ITM can be used for postoperative analgesia in pediatric surgery in all age groups, with no severe adverse events and high nurse satisfaction with analgesic management.