Objective: Our objective in the present study was to examine the temporal sequencing of posttraumatic and depressive symptoms during prolonged exposure therapy for posttraumatic stress disorder (PTSD) among children and adolescents. Method: Participants were 73 children and adolescents (56.2% female) between the ages of 8 and 18. Participants completed self-report measures of posttraumatic stress and depression prior to every session. Measures included the Child PTSD Symptom Scale, Beck Depression Inventory, and Children's Depression Inventory. Results: Multilevel mediational analyses indicated reciprocal relations during treatment: Changes in posttraumatic symptoms led to changes in depressive symptoms and vice versa. Posttraumatic symptoms accounted for 64.1% of the changes in depression, whereas depressive symptoms accounted for 11.0% of the changes in posttraumatic stress. Conclusions: Prolonged exposure therapy may work primarily by reducing posttraumatic stress, which in turn reduces depression. (Contains 3 footnotes, 3 tables, and 2 figures.)