Objective: Injury is the leading cause of death among American youth, killing more 11-year-olds than all other causes combined. Children with symptoms of externalizing behavior disorders such as attention-deficit/hyperactivity disorder (ADHD) and conduct disorder (CD) may have increased risk. Our aims were to determine: (1) whether increasing symptoms of ADHD and CD associate positively with injuries among a community sample of fifth graders; and (2) whether symptoms of ADHD and CD have a multiplicative rather than additive association with injuries among the sample. Methods: Data were collected from 4745 fifth graders and their primary caregivers participating in Healthy Passages, a multisite, community-based study of pediatric health risk behaviors and health outcomes. The primary outcome was injury frequency. Primary independent variables were ADHD and CD symptoms. Additional covariates included gender, race/ethnicity, and household income. Ordinal logistic regression examined correlates of injury frequency. The interaction between ADHD and CD symptoms also was examined. Results: In bivariate analyses, the odds of injury increased as ADHD symptoms (odds ratio [OR] 1.29; 95% confidence interval [95% CI] 1.18-1.41) and CD symptoms (OR 1.18; 95% CI 1.07-1.31) increased. However, in multivariate analysis, only ADHD symptoms were significantly associated with injury (OR 1.22; 95% CI 1.10-1.35). There was no statistically significant interaction between ADHD and CD symptoms. Conclusions: ADHD symptoms are associated with increased odds of injury in fifth graders. Findings have implications for potential injury prevention strategies for mental health practitioners (for example, cognitive training with at-risk youth), pediatricians (ADHD screening), and parents (improved supervision). Copyright © 2011 by Academic Pediatric Association.