To explore the reliability and validity of the Children's Impact of Event Scale (Chinese version, CRIES-13) and to determine the value and the optimal cutoff point of the score of CRIES-13 in screening posttraumatic stress disorder (PTSD), so as to provide evidence for PTSD prevention and identify children at risk in Wenchuan earthquake areas. A total of 253 children experienced the Wenchuan earthquake were tested through Stratified random cluster sampling. The authors examined CRIES-13's internal consistency, discriminative validity and predictive value of the cut-off. PTSD was assessed with the DSM-IV criteria. Area under the curve while sensitivity, specificity and Youden index were computed based on the receiver operating characteristic curve analysis. Optimal cutoff point was determined by the maximum of Youden index. 20.9% of the subjects were found to have met the DSM-IV criteria for PTSD 7 months after the Wenchuan earthquake accident. The Cronbach's coefficient of CRIES-13 was 0.903 and the mean inter-item correlation coefficients ranged from 0.283 to 0.689, the correlation coefficient of the three factors with the total scale scores ranged from 0.836 to 0.868 while the correlation coefficient among the three factors ranged from 0.568 to 0.718, PTSD cases indicated much higher scores than non-PTSD cases, the Youden index reached maximum value when the total score approached 18 in CRIES-13 with sensitivity and specificity as 81.1% and 76.5% respectively. Consistency check showed that there were no significant differences between the results of CRIES-13 score >/= 32 and clinical diagnosis (Kappa = 0.529) from the screening program. CRIES-13 appeared to be a reliable and valid measure for assessing the posttraumatic stress symptoms among children after the earthquake accident in the Wenchuan area. The CRIES-13 seemed to be a useful self-rating diagnostic instrument for survivors with PTSD symptoms as a clinical concern by using a 18 cut-off in total score. Consistency check showed that there was no significant difference between the screening result of CRIES-13 score >/= 32 and clinical diagnosis.