This chapter reviews the association between sleep-related breathing disorders (SRBDs) and cognitive functioning, depression, and anxiety. Obstructive sleep apnea (OSA) patients complain of various neuropsychiatric symptoms. Approximately 80% of OSA patients complain of both excessive daytime sleepiness and cognitive impairments, and half report personality changes. The pathogenesis of cognitive deficits in OSA is controversial and most likely multifactorial. Many studies have examined cognitive functioning after treatment for OSA has been initiated. Depression is the most commonly encountered affective disorder associated with OSA. As with cognitive impairment, sleep fragmentation and hypoxemia during sleep are suspected to be responsible for depressive symptoms in OSA. There is a growing literature suggesting that the links between depressive symptoms and OSA may be associated with obesity and the metabolic syndrome. Clinicians should suspect OSA particularly in depressed patients who present with symptoms such as snoring and excessive daytime fatigue.