Prior studies have argued that the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) criteria were insensitive for diagnosing posttraumatic stress disorder (PTSD) in young children. Four diagnostic criteria sets were examined in 284 3- to 6-year-old trauma-exposed children. The DSM-IV criteria resulted in significantly fewer cases (13%) compared to an alternative algorithm for young children (PTSD-AA, 45%), the proposed DSM-5 posttraumatic stress in preschool children (44%), and the DSM-5 criteria with 2 symptoms that are under consideration by the committee (DSM-5-UC, 49%). Using DSM-IV as the standard, the misclassification rate was 32% for PTSD-AA, 32% for DSM-5, and 37% for DSM-5-UC. The proposed criteria sets showed high agreement on the presence (100%), but low agreement on the absence (58–64%) of diagnoses. The misclassified cases were highly symptomatic, M = 7 or more symptoms, and functionally impaired, median = 2 domains impaired. The additional symptoms had little impact. Evidence for convergent validation for the proposed diagnoses was shown with elevations on comorbid disorders and Child Behavior Checklist Total scores compared to a control group (n = 46). When stratified by age (3–4 years and 5–6 years), diagnoses were still significantly elevated compared to controls. These findings lend support to a developmental subtype for PTSD.