OBJECTIVE: To critically review the literature concerning the effect of purposeful heading of a soccer ball and head injuries on reported cognitive dysfunction in soccer players. DATA SOURCES: We searched MEDLINE (1965-2001) and SPORTDiscus (1975-2001) for refereed articles in English combining key words for soccer (eg, soccer, football, association football ) with key words for head injuries (eg, concussion, head injury). In addition, literature on cognition and head injuries was obtained. We reviewed reference lists of current literature for pertinent citations that might not have been found in the search procedures. DATA SYNTHESIS: The fact that soccer players (and other athletes) have selected cognitive deficits is not questioned, and the popular press is quick to publicize results of questionable validity. The reasons for such deficits are many. Much of the early data implied that heading was the culprit; however, subsequent research has suggested that other interpretations and factors may be potential explanations for these deficits. The current focus is on concussions, a known factor in cognitive dysfunction and a common head injury in soccer. CONCLUSIONS/RECOMMENDATIONS: It is difficult to blame purposeful heading for the reported cognitive deficits when actual heading exposure and details of the nature of head-ball impact are unknown. Concussions are a common head injury in soccer (mostly from head-head or head-ground impact) and a factor in cognitive deficits and are probably the mechanism of the reported dysfunction.