The sequelae of severe closed head injury have received much attention in the literature, but the effects of mild closed head injury (MHI) are less well established. There is a subgroup of patients who complain of persisting postconcussive symptoms (PCS) beyond the first weeks of recovery. Although the symptoms generally develop in the absence of clear neurological abnormalities, the condition of PCS can be chronic and disabling. It has been assumed that PCS result from an interaction between organic and psychological factors. Differentiating between the effect of primary neurological injury and secondary psychosocial problems is often difficult for clinicians and engenders controversy. Neuropsychological, neurophysiological, and neuroimaging measures can be helpful in selecting patients at risk of developing PCS. Assessment of the level of cognitive functioning, individual susceptibility to stress, and environmental demands may be beneficial in treating symptomatic patients. It is true that the vague and aspecific nature of the postconcussion syndrome may have given rise to the controversy over this entity, but the many methodological inconsistencies in the experimental approaches to the syndrome have certainly enhanced the confusion about this issue. The ensuing controversy surrounding research on the outcome of MHI and the postconcussion syndrome reflects ambiguities in definition, inconsistencies in criteria for patient selection, variation in procedures for neurobehavioral assessment, and difficulty in obtaining follow-up data.