The Panic Disorder Severity Scale (PDSS; Shear et al., 1997) is a well-validated measure that assesses symptoms of panic disorder with or without agoraphobia (PDA) in adults. The Panic Disorder Severity Scale for Children (PDSS-C) is an adaptation of the PDSS for youth ages 11-17. The current study evaluated the psychometric properties of the PDSS-C. Participants included 60 adolescents from a randomized controlled trial investigating the efficacy of an intensive cognitive behavioral treatment (CBT) for adolescent PDA. Convergent and discriminant validity of PDSS-C scores were evaluated via observed associations between the PDSS-C and the Childhood Anxiety Sensitivity Index (CASI; Silverman, Fleisig, Rabian, & Peterson, 1991), Multidimensional Anxiety Scale for Children (MASC; March, Parker, Sullivan, Stallings, & Conners, 1997), and Children's Depression Inventory (CDI; Kovacs, 2003). Baseline and posttreatment data afforded the opportunity to evaluate the measure's sensitivity to treatment-related change. PDSS-C scores demonstrated acceptable internal consistency (α = .82) and adequate 1-day test-retest reliability (r = .79). Convergent and discriminant validity of the PDSS-C scores were supported through significant associations with the CASI and the MASC, and nonsignificant associations with the CDI, respectively. Linear regression analysis demonstrated sensitivity to treatment-related changes-that is, greater PDSS-C change scores were significantly associated with assignment to CBT vs. waitlist condition. Clinical utility was further established through significant associations between PDSS-C change scores and MASC and CASI change scores, and through nonsignificant associations with CDI change scores. Results support the use of PDSS-C scores as reliable, valid, and clinically useful for the assessment of youth panic disorder in research and clinical settings.