The purpose of the study was to investigate the impact of aerobic exercise on the severity of symptoms of Posttraumatic Stress Disorder (PTSD), depression, and anxiety. Twelve institutionalized female adolescents completed a 15-session aerobic exercise program consisting of moderate-intensity walking. All participants completed the Child PTSD Symptom Scale (CPSS), Trauma Symptom Checklist for Children (TSCC), Multidimensional Anxiety Scale for Children (MASC), and Children's Depression Inventory (CDI) twice at pretest. Data were collected twice during an extended baseline period, at postintervention, and again at a 1-month follow-up assessment. Yarnolds (1988) ipsative z-score comparison method for single-case repeated measures design was utilized in data analysis for participants with stable levels of symptomatology during baseline. Strong effects of aerobic exercise were found for PTSD and trauma symptom severity but not for anxiety and depressive symptom severity. Follow-up results were mixed. The results of this study were fairly consistent with previous research findings. Strong effects of aerobic exercise on depression and anxiety were not found; however, relatively low levels of such symptomatology had been noted for many participants during the baseline phase of the study.