Persistent cognitive complaints are common following a mild head injury (MHI), but deficits are rarely detected on neuropsychological tests. Our objective was to examine the effect of symptom expectation on self-report and cognitive performance measures in MHI individuals. Prior research suggests that when MHI participants are informed they may experience cognitive difficulties, they perform worse on neuropsychological tests compared to MHI participants who are uninformed. In this study, undergraduate students with and without a prior MHI were either informed that the study's purpose was to investigate the effects of MHI on cognitive functioning ("diagnosis threat" condition) or merely informed that their cognitive functioning was being examined, with no mention of status ("neutral" condition). "Diagnosis threat" MHIs self-reported more attention failures compared to "diagnosis threat" controls and "neutral" MHIs, and more memory failures compared to "diagnosis threat" controls. In the "neutral" condition, MHIs reported higher anxiety levels compared to controls and compared to "diagnosis threat" MHIs. Regardless of condition, MHIs performed worse on only one neuropsychological test of attention span. "Diagnosis threat" may contribute to the prevalence and persistence of cognitive complaints made by MHI individuals found in the literature, but may not have as strong of an effect on neuropsychological measures.