OBJECTIVES:: To examine the frequency and nature of postconcussive symptoms (PCSs) and behavioral outcomes in young children following mild traumatic brain injury (mTBI) or concussion. SETTING:: Emergency department. PARTICIPANTS:: Children aged 2 to 12 years presenting with either a concussion or minor bodily injury (control). OUTCOME MEASUREMENT:: Parent ratings of PCS were obtained within 72 hours of injury, at 1 week, and 1, 2, and 3 months postinjury using a comprehensive PCS checklist. Preinjury behavior was examined at baseline using the Clinical Assessment of Behavior, which was readministered 1 and 3 months postinjury. RESULTS:: PCS burden following mTBI peaked in the acute phase postinjury but reduced significantly from 1 week to 1 month postinjury. Parents of children with mTBI reported more persistent PCSs up to 3 months postinjury than trauma controls, characterized mostly by behavioral and sleep-related symptoms. Subtle increases in problematic behaviors were observed from baseline (preinjury) to 1 month postinjury and persisted at 3 months postinjury; however, scores were not classified as clinically “at risk.” CONCLUSIONS:: A significant minority of young children experienced persistent PCS and problematic behavior following mTBI. Care must be taken when assessing PCS in younger children as method of PCS assessment may influence parental reporting.