In this preliminary, 12-week open-label study, eight adolescents with moderate to severe post-traumatic stress disorder (PTSD) were treated with citalopram (the most selective of the selective serotonin reuptake inhibitors) in a fixed daily dose of 20 mg, and rated at 2-week intervals. The Clinician-Administered PTSD Scale (Child and Adolescent Version) was the primary measure used to assess treatment outcome. Core PTSD symptoms (re-experiencing, avoidance, and hyperarousal symptoms) showed statistically significant improvement at week 12 on the Clinician-Administered PTSD Scale (Child and Adolescent Version) (CAPS-CA), with a 38% reduction in total CAPS scores between baseline and endpoint. Citalopram failed to effect improvement on self-reported depressive symptoms. All seven adolescent completers were rated as much improved or very much improved on Clinical Global Impression Improvement scores. Citalopram was well-tolerated overall with reported adverse experiences being relatively benign. However, larger, controlled trials are needed to consolidate these preliminary results.