Sleep disorders are common in patients with traumatic brain injury and may occur in all stages of recovery. Sleep disorders are found in 36%-81.2% of recently traumatized inpatients and 72 7% of discharged patients. Sleep onset and sleep maintenance disorders were more common in patients hospitalized with recent traumatic brain injury, and narcolepsy was more common in patients in the subacute phase. The total cost of treating insomnia in the United States exceeds $100 billion annually when the low productivity and accidents associated with insomnia are taken into account. Patients with traumatic brain injury typically experience difficulties in many aspects of life, including personal, professional, social, and hobby aspects, and insomnia and sleep disorders can exacerbate life difficulties due to the negative shagging effects of sleep disorders on both behavior and cognitive abilities. Insomnia in non-traumatic brain injury patients has been correlated with increased absenteeism, increased health care utilization, and social functioning deficits. I. Definition of insomnia Primary insomnia is insomnia that is not related to medical, psychiatric or environmental factors. More commonly, secondary insomnia is caused by underlying medical, psychiatric, or environmental factors. Acute insomnia is insomnia caused by emotional or somatic discomfort. Acute insomnia can be considered a subtype of secondary insomnia. Difficult-to-sleep insomnia is a condition in which the time between going to bed and falling asleep is prolonged. Disturbed circadian rhythm of sleep is a subtype of dysphoric insomnia. The international classification of sleep disorders classifies sleep disorders into sleep disorders that lead to insomnia or excessive sleepiness; heterosomnia, which is a disorder of wakefulness, partial wakefulness or change between sleep periods; and sleep disorders related to diseases or psychological disorders. An extensive review and overview of physical conditions that may cause insomnia is not the focus of this chapter, but patients with sleep disorders should consider a combination of medical factors. Classification of sleep apnea: obstructive sleep apnea, central sleep apnea and mixed sleep apnea. Obstructive sleep apnea is characterized by the presence of thoracoabdominal breathing action due to upper airway obstruction or pharyngeal collapse, and the characteristic periodic apnea and asphyxia formed by the continuous ineffective respiratory action. Central sleep apnea is the simultaneous cessation of upper airway airflow and thoracoabdominal respiratory actions. Mixed sleep apnea has various manifestations of both obstructive sleep apnea and central sleep apnea. Symptoms associated with sleep apnea include excessive daytime sleepiness and impaired cognitive functions such as memory loss, loss of judgment, inability to concentrate, and irritability and depression. These symptoms are commonly seen in patients with traumatic brain injury that is not associated with sleep apnea, making clinical diagnosis very difficult. Secondary cardiovascular diseases associated with sleep apnea include hypertension and pulmonary hypertension, cardiac arrhythmias, pulmonary heart disease, stroke, and sudden death. Electrolyte disturbances, hydrocephalus, occult infections, seizures, and endocrine disorders can also contribute to fatigue and excessive daytime sleepiness in patients with traumatic brain injury.