This study investigated the existing diagnostic algorithms for posttraumatic stress disorder (PTSD) to determine the most developmentally sensitive and valid approach for diagnosing this disorder in preschoolers. Participants were 130 parents of unintentionally burned children (1-6 years). Diagnostic interviews were conducted with parents to assess for PTSD in their child at 1 and 6 months postinjury and the Child Behavior Checklist for 1.5-5 was also completed. The proposed algorithm for PTSD in preschool children for the "Diagnostic and Statistical Manual of Mental Disorders" (5th ed.) provided the most developmentally sensitive and valid measure of PTSD. The rate of PTSD diagnosis was 25% at 1 month and 10% at 6 months. The predictive utility of Criterion A was not demonstrated. These findings provide support for the inclusion of the proposed algorithm for PTSD in preschool children. (Contains 4 tables.)