Pain-related functional limitations represent an important outcome domain to assess in children and adolescents with chronic pain. The aim of this study was to extend the empirical support of the 21-item Child Activity Limitations Interview (CALI-21), a well-validated measure of activity limitations, using a large, multisite sample and to develop a brief form of the measure with more interpretable scoring. A sample of 1616 youth and 1614 parents completed the CALI-21 at an initial appointment in 1 of 3 pain specialty clinics in the Midwest or Northwest United States, or as part of a research study after this initial visit. All youth also reported on usual pain intensity. The CALI-21 data from 1236 youth and parents were used in analyses. Results of the exploratory and confirmatory factor analyses supported a common 2-factor structure (Active and Routine factors) for both child- and parent-report versions. Using item reduction, the 9-item measure (CALI-9) was developed with both child and parent versions showing good internal consistency and high cross-informant reliability. Initial validity was shown by the ability of the CALI-9 to distinguish by level of pain intensity. Findings suggest that the CALI-9 is a promising brief tool for the evaluation of pain-related activity limitations in youth with chronic pain and for proxy report by parents. Advantages of the shortened scale include the revised 0 to 100-point scale, which increases interpretability, and further validation of the subscale scoring to assess specific limitations in Active and Routine physical functioning domains.