PRIMARY OBJECTIVE To examine the frequency of acute mild traumatic brain injury (mTBI) symptoms in children using a concussion symptom inventory and to identify which symptoms are most useful in identifying mTBI. It was hypothesized that symptoms associated with mTBI are more common in children with head injury than orthopaedic injury and certain symptoms are more useful than others in identifying mTBI. RESEARCH DESIGN Prospective case-control study conducted in a paediatric trauma centre emergency department. METHODS AND PROCEDURES Children of 6-18 years old with head injury or a minor extremity injury were enrolled. Symptoms were assessed using a graded symptom checklist. Symptom frequency was compared using a chi-square test. The association between individual symptoms with AMS was evaluated with logistic regression analysis. MAIN OUTCOMES AND RESULTS Children with head injury displayed more frequent symptoms than controls. Head-injured cases with altered mental status (AMS) demonstrated the most frequent and severe symptoms (median symptom scores: control = 1, cases without AMS = 5, cases with AMS = 10; p < 0.001). Headache, nausea, dizziness, blurred/double vision and not feeling 'sharp' were associated with AMS. CONCLUSIONS Symptoms associated with mTBI are more frequent in children with head injury. AMS magnifies this effect. A symptom inventory is integral to the evaluation of mTBI in children; a smaller set of dichotomized symptoms may be as useful as and more easily administered than lengthier symptom scales.