Context: Although the prevalence of invalid baseline neu- rocognitive testing has been documented, and repeated administration after obtaining invalid results is recommended, no empirical data are available on the utility of repeated assessment after obtaining invalid baseline results. Objective: To document the utility of readministering neurocognitive testing after an invalid baseline test. Design: Case series. Setting: Schools, colleges, and universities. Patients or Other Participants: A total of 156 athletes who obtained invalid results on ImPACT baseline neurocognitive testing and were readministered the ImPACT baseline test within a 2-week period (mean 1⁄4 4 days). Main Outcome Measure(s): Overall prevalence of invalid results on reassessment, specific invalidity indicators at initial and follow-up baseline, dependent-samples analysis of vari- ance, with Bonferroni correction for multiple comparisons. Results: Reassessment resulted in valid test results for 87.2% of the sample. Poor performance on the Design Memory and Three-Letter subscales were the most common reasons for athletes obtaining an invalid baseline result, on both the initial assessment and the reassessment. Significant improvements were noted on all ImPACT composite scores except for Reaction Time on reassessment. Of note, 40% of athletes showed slower reaction time scores on reassessment, perhaps reflecting a more cautious approach taken the second time. Invalid results were more likely to be obtained by athletes with a self-reported history of attention-deficit disorder or learning disability on reassessments (35%) than on initial baseline assessments (10%). Conclusions: Repeat assessment after the initial invalid baseline performance yielded valid results in nearly 90% of cases. Invalid results on a follow-up assessment may be influenced by a history of attention-deficit disorder or learning disability, the skills and abilities of the individual, or a particular test-taking approach; in these cases, a third assessment may not be useful.