Objective: To identify latent classes of posttraumatic stress disorder (PTSD) symptoms in a national sample of adolescents, and to test their associations with PTSD and functional impairment 1 year later. Method: A total of 1,119 trauma-exposed youth aged 12 through 17 years (mean = 14.99 years, 51% female and 49% male) participating in the National Survey of Adolescents--Replication were included in this study. Telephone interviews were conducted to assess PTSD symptoms and functional impairment at Waves 1 and 2. Results: Latent Class Analysis revealed three classes of adolescent PTSD at each time point: pervasive disturbance, intermediate disturbance, and no disturbance. Three numbing and two hyperarousal symptoms best distinguished the pervasive and intermediate disturbance classes at Wave 1. Three re-experiencing, one avoidance, and one hyperarousal symptom best distinguished these classes at Wave 2. The Wave 1 intermediate disturbance class was less likely to have a PTSD diagnosis, belong to the Wave 2 pervasive disturbance class, and report functional impairment 1 year later compared with the Wave 1 pervasive disturbance class. The Wave 1 no disturbance class was least likely to have PTSD, belong to the pervasive disturbance class, and report functional impairment at Wave 2. Conclusions: This study suggests that PTSD severity-distinguishing symptoms change substantially in adolescence and are not characterized by the numbing cluster, contrary to studies in adult samples. These results may help to explain inconsistent factor analytic findings on the structure and diagnosis of PTSD, and emphasize that developmental context is critical to consider in both research and clinical work in PTSD assessment and diagnosis. (Contains 4 tables and 1 figure.)