The postconcussion syndrome refers to a large number of symptoms and signs that may occur alone or in combination following usually mild head injury. The most common complaints are headaches, dizziness, fatigue, irritability, anxiety, insomnia, loss of consciousness and memory, and noise sensitivity. Mild head injury is a major public health concern because the annual incidence is about 150 per 100,000 population, accounting for 75% or more of all head injuries. The postconcussion syndrome has been recognized for at least the last few hundred years and has been the subject of intense controversy for more than 100 years. The Hollywood head injury myth has been an important contributor to persisting skepticism and might be countered by educational efforts and counter-examples from boxing. The organicity of the postconcussion syndrome has now become well documented. Abnormalities following mild head injury have been reported in neuropathologic, neurophysiologic, neuroimaging, and neuropsychologic studies. There are multiple sequelae of mild head injury, including headaches of multiple types, cranial nerve symptoms and signs, psychologic and somatic complaints, and cognitive impairment. Rare sequelae include hematomas, seizures, transient global amnesia, tremor, and dystonia. Neuroimaging and physiologic and psychologic testing should be used judiciously based on the problems of the particular patient rather than in a cookbook fashion. Prognostic studies clearly substantiate the existence of a postconcussion syndrome. Manifestations of the postconcussion syndrome are common, with resolution in most patients by 3 to 6 months after the injury. Persistent symptoms and cognitive deficits are present in a distinct minority of patients for additional months or years. Risk factors for persisting sequelae include age over 40 years; lower educational, intellectual, and socioeconomic level; female gender; alcohol abuse; prior head injury; and multiple trauma. Although a small minority are malingerers, frauds, or have compensation neurosis, most patients have genuine complaints. Contrary to a popular perception, most patients with litigation or compensation claims are not cured by a verdict. Treatment is individualized depending on the specific complaints of the patient. Although a variety of medication and psychologic treatments are currently available, ongoing basic and clinical research of all aspects of mild head injury are crucial to provide more efficacious treatment in the future.