Trauma exposure and posttraumatic stress disorder (PTSD), though prevalent among adolescent psychiatric inpatients, are underidentified in standard clinical practice. In a retrospective chart review of 140 adolescents admitted to a psychiatric inpatient unit, we examined associations between probable PTSD identified through the Child PTSD Symptom Scale and adolescents' service use and clinical characteristics. Results suggest a large discrepancy between rates of probable PTSD identified through standardized assessment and during the emergency room psychiatric evaluation (28.6% vs. 2.2%). Adolescents with probable PTSD had greater clinical severity and service utilization, an increased likelihood of being diagnosed with bipolar disorder (27.5% vs. 9.2%) and being prescribed antipsychotic medications (47.5% vs. 27.6%), and were prescribed more psychotropic medications. Upon discharge, those with probable PTSD were more than those without to be assigned a diagnosis of PTSD (45% vs. 7.1%), a comorbid diagnosis of major depressive disorder (30% vs. 14.3%), to be prescribed an antidepressant medication (52.5% vs. 33.7%), and to be prescribed more medications. The underidentification of trauma exposure and PTSD has important implications for the care of adolescents given that accurate diagnosis is a prerequisite for providing effective care. Improved methods for identifying trauma-related problems in standard clinical practice are needed.