CONTEXT: Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) is a computerized cognitive test battery commonly used for concussion evaluation. An important aspect of these procedures is baseline testing, but researchers have suggested that many users do not use validity indices to ensure adequate effort during testing. No one has examined the prevalence of invalid performance for college football players. OBJECTIVE: To examine the prevalence of invalid scores on ImPACT testing. DESIGN: Cross-sectional study. SETTING: National Collegiate Athletic Association Division I university. PATIENTS OR OTHER PARTICIPANTS: A total of 159 athletes (age = 20.3 +/- 1.41 years; range = 17.8-23.7 years) from a Division I collegiate football team participated. INTERVENTION(S): An informational intervention regarding the importance of concussion testing to promote safety was administered before testing for the most recent season. MAIN OUTCOME MEASURE(S): We examined preseason ImPACT testing data across a 3-year period (total assessments = 269). Based on invalid and sandbagging indices denoted by the ImPACT manual, protocols were examined to indicate how many invalid indices each athlete had. RESULTS: A total of 27.9% (n = 75) of assessments were suggestive of invalid scores, with 4.1% (n = 11) suggesting invalid responding only, 17.5% (n = 47) indicating “sandbagging” only, and 6.3% (n = 17) showing both invalid and sandbagging responding. The informational intervention did not reduce the prevalence of invalid responding. CONCLUSIONS: These findings highlight the need for further information about the ImPACT validity indices and whether they truly reflect poor effort. Future work is needed to identify practices to reliably target and reduce invalid responding.