Objective: The purpose of this study is to compare postoperative pain scores between children undergoing tonsillectomy and adenoidectomy (T&A) surgery and their parents, identify potential predictors for this disagreement, and determine possible impact on analgesic administration. Methods: This is a prospective longitudinal study conducted with children undergoing outpatient T&A in 4 major tertiary hospitals and their parents. Children and their parents were enrolled prior to surgery and completed baseline psychological instruments assessing parental anxiety (STAI), parental coping style (MBSS), child temperament (EAS) and parental medication administration attitude questionnaire (MAQ). Postoperatively, parents and children completed at-home pain severity ratings (Faces Pain Scale-Revised, children; Numeric Rating Scale, parents) on postoperative recovery days 1, 2, and 3, reflecting an overall pain level for the past 24 hours. Parents also completed a log of analgesic administration. Based on postoperative pain scores, parent-child dyads were classified as overestimators (i.e., parents rated their child's pain higher than children rated their own pain), in agreement (i.e., rating in agreement), or underestimators (i.e., parents rated their child's pain lower than children rated their own pain). Results: A significant proportion of parent-child pairs disagreed on pain ratings on postoperative days 1-3 (30.05%-35.95%). Of those pairs in disagreement, the majority of parents overestimated their child's pain on all three postoperative days, specifically such that a total of 24-26% parents overestimated their child's pain on postoperative days 1, 2, and 3. Repeated measures ANOVA 19 demonstrated that parents in the overestimator group administered higher, though still within safe 20 limits, amounts of ibuprofen and oxycodone (mg/day) than did the underestimator or agreement 21 groups. Multiple regression models showed hospital site as the only independent predictor for 22 postoperative pain rating disagreement between children and parents. 23 2 Conclusions: Since parents overestimate their child's postoperative pain and may administer more analgesics to their child, it is essential to develop a standardized method of child pain assessment and a tailored recommended postoperative analgesic regimen amongst medical providers for children undergoing T&A.