Objective: To describe the prevalence of acute stress disorder (ASD) symptoms and to examine proposed DSM-5 symptom criteria in relation to concurrent functional impairment in children and adolescents. Method: From an international archive, datasets were identified that included assessment of acute traumatic stress reactions and concurrent impairment in children and adolescents 5 to 17 years of age. Data came from 15 studies conducted in the United States, United Kingdom, Australia, and Switzerland and included 1,645 children and adolescents. Dichotomized items were created to indicate the presence or absence of each of the 14 proposed ASD symptoms and functional impairment. The performance of a proposed diagnostic criterion (number of ASD symptoms required) was examined as a predictor of concurrent impairment. Results: Each ASD symptom was endorsed by 14% to 51% of children and adolescents; 41% reported clinically relevant impairment. Children and adolescents reported from 0 to 13 symptoms (mean = 3.6). Individual ASD symptoms were associated with greater likelihood of functional impairment. The DSM-5 proposed eight-symptom requirement was met by 202 individuals (12.3%) and had low sensitivity (0.25) in predicting concurrent clinically relevant impairment. Requiring fewer symptoms (three to four) greatly improved sensitivity while maintaining moderate specificity. Conclusions: This group of symptoms appears to capture aspects of traumatic stress reactions that can create distress and interfere with children's and adolescents' ability to function in the acute post-trauma phase. Results provide a benchmark for comparison with adult samples; a smaller proportion of children and adolescents met the eight-symptom criterion than reported for adults. Symptom requirements for the ASD diagnosis may need to be lowered to optimally identify children and adolescents whose acute distress warrants clinical attention.