Traumatic experiences are common among youths and can lead to posttraumatic stress disorder (PTSD). In order to identify traumatized children who need PTSD treatment, instruments that can accurately and efficiently evaluate pediatric PTSD are needed. One such measure is the Child PTSD Symptom Scale (CPSS), which has been found to be a reliable and valid measure of PTSD symptom severity in school-age children exposed to natural disasters (Foa, Johnson, Feeny, & Treadwell, 2001). However, the psychometric properties of the CPSS are not known in youths who have experienced other types of trauma. The current study aims to fill this gap by examining the psychometric properties of the interview (CPSS-I) and self-report (CPSS-SR) administrations of the CPSS in a sample of 91 female youths with sexual abuse-related PTSD, a population that is targeted in many treatment studies. Scores on both the CPSS-I and CPSS-SR demonstrated good to excellent internal consistency. One-week test–retest reliability assessed for CPSS-SR scores was excellent (r = .86); interrater reliability of CPSS-I scores was also excellent (r = .87). Symptom-based diagnostic agreement between the CPSS-SR and CPSS-I was excellent at 85.5%; scores on both the CPSS-SR and CPSS-I also demonstrated good convergent validity (74.5–76.5% agreement) with the PTSD module of The Schedule of Affective Disorders and Schizophrenia for School-Age Children–Revised for DSM–IV (K-SADS; Kaufman, Birmaher, Brent, & Rao, 1997). The strong psychometric properties of the CPSS render it a valuable instrument for PTSD screening as well as for assessing symptom severity.