Mild head trauma is often complicated by a persistent set of symptoms known as postconcussion syndrome (PCS). Past research has suggested that an expectancy-guided, retrospective-recall bias may account for much of the variance in PCS symptom reporting. The present study examined the influence of symptom expectations on mild head trauma symptom reports among participants in contact sports. Head-injured athletes reported symptom rates that did not differ from those of uninjured athletes but consistently underestimated the preinjury incidence of symptoms. Athletes with no head trauma history overestimated the expected degree of pre- to postinjury change in symptom status. Results suggest that individuals with mild head injury tend to overestimate postconcussion symptom change in a manner consistent with their symptom expectations. A cognitive-behavioral model that explains the persistence of PCS is proposed.