Half of children admitted after surgery experience intense pain in hospital, and many experience continued pain and delayed functional recovery at home. However, there is a gap in tools available to measure acute functional ability in pediatric postsurgical settings. We aimed to validate the Youth Acute Pain Functional Ability Questionnaire (YAPFAQ) in a large inpatient pediatric surgical population, evaluate its responsiveness to expected functional recovery, and develop a short form for broad clinical implementation. The YAPFAQ is a self-report measure assessing acute functional ability, developed in children admitted for acute sickle cell pain. We evaluated psychometric properties of the measure in 564 children ages 8 to 18 years admitted after surgery. A sample of 54 participants completed the YAPFAQ daily for 3 days after major surgery to assess responsiveness. The measure showed good reliability (Cronbach alpha = .96) and construct validity, with expected relationships with physical health-related quality of life (r = -.53, P < .001) and pain intensity (r = .42, P < .001). YAPFAQ scores decreased over time showing good responsiveness to expected recovery. A 3-item short form of the YAPFAQ showed promising psychometric properties. Early assessment of functioning after surgery may identify children at risk for poor functional outcomes and allow targeting of therapies to improve postsurgical recovery. PERSPECTIVE: The YAPFAQ showed promising psychometric properties in a pediatric postsurgical population. This study addresses a gap in tools available to monitor functional recovery during hospitalization after pediatric surgery. Early detection of problems with recovery may enable targeted therapies to improve postsurgical outcomes.