Mild head injuries can cause acute transient cognitive inefficiency that typically resolves within 3 months. Postconcussion syndrome may initially be related to acute cerebral dysfunction but can also arise as a psychological consequence of head trauma. The syndrome persists beyond 3 months in a significant number of patients with mild head trauma as a psychological disorder. International Classification of Diseases diagnostic criteria for postconcussion syndrome are currently recommended for clinical purposes. These criteria are contrasted with research diagnostic criteria used in the Diagnostic and Statistical Manual of Mental Disorders. The differential diagnosis of persistent cognitive and postconcussive symptoms in forensic practice is reviewed.