Background and Objective: Children with cognitive impairment (CI) are at risk of experiencing pain. Several specific pain rating scales have been developed to date. Thus, the aim of this meta-analysis was to estimate the degree of reliability of different pain assessment scales for the postoperative pain in children with CI. Databases and DataTreatment: PubMed, Scopus and Web of Science databases were approached: all studies validating and/or using pain assessment tool in children (0-20 years) with CI published in English from the 1st of January 2000 to the 1st of January 2022 were included. Only studies reporting the interclass correlation coefficient (ICC) to evaluate the concordance between caregivers' and external researchers' scores were eligible. Results: Twelve studies were included (586 children with CI, 60% males; weighted mean age 9.9 years -range 2-20). Five of them evaluated the Non-Communicating Children's Pain Checklist-Postoperative Version (NCCPC-PV)scale whereas four the original and revised Face, Legs, Activity, Cry, Consolability (FLACC) scale. The analysis showed an overall ICC value of 0.76 (0.74-0.78) for the NCCPC-PV scale, with a high heterogeneity index (I 2 = 97%) and 0.87 (0.84-0.90) for the FLACC scale, with a discrete I 2 index (59%). Conclusions:The NCCPC-PV and FLACC pain rating scales showed the strongest evidence for validity and reliability for assessing postoperative pain in children with CI. However, due to the high heterogeneity of the studies available, these results should not be considered conclusive.Significance: This review is focused on the assessment of pain in children with CI in the postoperative period. Simplified observation-based pain assessment tools that rely on evaluating non-verbal expressions of pain should be recommended for children with difficulties to communicate their feelings. Even if there is a high degree of heterogeneity in clinical presentations among youth with CI,