The present study examined the effect of negative expectations on neuropsychological test performance. It was hypothesized that having attention called to a history of prior head injury and the potential effects of head injury on cognition would result in diminished neuropsychological test performance relative to individuals with a similar head injury history but who did not have their attention called to their head injury history ('diagnosis threat'). Of 36 participants with a history of mild head injury, 17 were randomly assigned to diagnosis threat and 19 to neutral test directions. The diagnosis threat group performed significantly worse on tests measuring general intellect and memory, but were not different from the neutral group in basic attention or psychomotor speed. The diagnosis threat group rated themselves as putting forth less effort on the neuropsychological battery, and self-rated effort correlated with test performance in that group. Overall, results serve as a reminder that neuropsychological tests are measures of behavior, and thus can be influenced by nonneurological factors.