Children and adolescents experience high rates of potentially traumatic experiences. Many children subsequently develop mental health problems, including post-traumatic stress disorder (PTSD) symptoms. Accurately diagnosing PTSD in children is challenging. This paper reviews the following important issues: (i) the specificity of the PTSD diagnosis; (ii) children who are symptomatic and impaired but do not have enough symptoms for the diagnosis of PTSD; (iii) developmental considerations for preschool and school-age children; and (iv) a variety of assessment challenges that reflect the difficulty and complexity of interviewing children and caregivers about these symptoms. Despite these challenges, PTSD remains the best construct for clinical and research work with trauma survivors. Pediatric PTSD criteria are valuable for identifying children at risk and in need of treatment, and can be even more helpful when developmentally modified in ways that are discussed.