Purpose: The usefulness of the Patient State Index (PSI), an electroencephalogram (EEG)-based tool recently introduced in pediatric critical care units (PICU) , and the clinical level of sedation has not been yet demonstrated in pediatric critical care patients. This study investigated the association between the Patient State Index (PSI) and the Richmond Agitation–Sedation Scale (RASS) in PICU patients to determine whether the PSI could serve as a reliable objective measure of sedation in critically ill children. Setting: a pediatric intensive care unit of a tertiary hospital. Methods: This prospective observational study continuously monitored PSI values using the SedLine® monitor (Masimo, Irvine, CA, USA). Monitoring began at the initiation of sedative therapy and continued for up to 2 hours after its discontinuation. PSI values were recorded immediately before each Richmond Agitation–Sedation Scale (RASS) assessment, which was performed by the attending physicians at the start of sedative therapy, at 6, 12, and 24 hours thereafter, and immediately before sedation withdrawal. Results: A total of 87 paired PSI and RASS measurements were obtained from 35 patients. The PSI showed a weak positive correlation with the RASS score (Spearman's rank correlation coefficient = 0.26; 95% confidence interval [CI], 0.049–0.467; p = 0.01). Agreement between the PSI and RASS was slight, with a Cohen's kappa coefficient of 0.14 (95% CI, 0.067–0.348; p = 0.09). PSI values did not differ significantly across RASS categories (Kruskal–Wallis test, p = 0.166). Receiver operating characteristic (ROC) curve analysis identified a PSI threshold of 39 for distinguishing light sedation (RASS ≥ −2) from deep sedation (RASS ≤ −3). The area under the ROC curve was 0.65 (95% CI, 0.534–0.766), with a sensitivity of 0.68 and a specificity of 2.38. Conclusions: The PSI showed only a weak correlation with the RASS in critically ill children. Therefore, it should be used cautiously as a standalone measure of sedation depth in the PICU. However, these findings do not negate its potential clinical value. Instead, the PSI should be interpreted as part of a multimodal neuromonitoring strategy, taking into account age-related EEG maturation, the clinical context, and the known limitations of EEG-derived indices in critically ill patients.