Objective: To examine the frequency of behavioral problems after childhood traumatic brain injury (TBI) and their associations with injury severity, sex, and social environmental factors. Setting: Children's hospitals in the Midwestern/Western United States. Participants: 381 boys and 210 girls with moderate (n = 359) and severe (n = 227) TBI, with an average age at injury of 11.7 years (range 0.3-18) who were injured ≤3 years ago. Design: Secondary data analysis of a multistudy cohort. Main Measures: Child Behavior Checklist (CBCL) administered pretreatment. Results: Thirty-seven percent had borderline/clinical elevations on the CBCL Total Problem Scale, with comparable rates of Internalizing and Externalizing problems (33% and 31%, respectively). Less parental education was associated with higher rates of internalizing, externalizing, and total problems. Time since injury had a linear association with internalizing symptoms, with greater symptoms at longer postinjury intervals. Younger boys had significantly higher levels of oppositional defiant symptoms than girls, whereas older girls had significantly greater attention-deficit hyperactivity disorder symptoms than boys. Conclusions: Pediatric TBI is associated with high rates of behavior problems, with lower socioeconomic status predicting substantially elevated risk. Associations of higher levels of internalizing symptoms with greater time since injury highlight the importance of tracking children over time.