More than 35 million American children ages 5 to 18 and approximately 400,000 collegiate athletes engage in organized sports. Sport participation bears a risk of traumatic brain injury (TBI). The annual incidence of sport-related TBI exceeds 1.5 million and is increasing among youth athletes. Many sufferers of TBI present with co-occurring psychiatric conditions, such as anxiety, depression, and learning disabilities. The effect of these conditions on diagnosis and prognosis remains largely unexplored. PURPOSE: To assess the effect of co-occurring conditions on TBI symptoms in youth athletes. METHODS: We analyzed 80 student-athletes (primary education through college) who underwent comprehensive evaluation following a TBI. Medical histories were collected, neuropsychological tests were conducted, and co-occurring psychiatric conditions were diagnosed. Co-occurring conditions were 1) attention deficit and hyperactivity disorders, 2) anxiety disorders, 3) depression and mood disorders, 4) adjustment disorders, and learning disabilities. Tests of behavior and cognitive function were 1) the ImPACT test, and 2) the Behavior Assessment System for Children 2nd Edition (BASC). Linear regressions tested the effect of co-occurring conditions on psychological and behavioral outcomes. RESULTS: Subjects were 16.0 ± 2.6 years of age, 56.3% were male, and 72.5% were diagnosed with ≥1 co-occurring condition. Linear regressions revealed the number of diagnoses to predict poorer visual motor speed (p=0.031), poorer reaction time (p=0.010), and, summarizing speed and accuracy indices, poorer performance on the cognitive efficiency index (p=0.043). The number of co-occurring conditions was also a significant predictor (p<0.05) of 13 individual BASC categories and all BASC composite assessments, indicating poorer behaviors and attitudes. CONCLUSION: TBI associates with acute neural deficits and psychological changes. We found that co-occurring psychiatric diagnoses may compound these complications in youth athletes. When appraising the severity of a TBI in this population, a comprehensive psychiatric evaluation may be warranted to understand and accurately characterize the scope and prognosis of the condition.