The prognosis of sleep apnea syndrome (SAS) is dominated by cardiovascular complications. However, this disease is concerned with psychiatric field through specific clinical patterns. Nocturnal respiratory arrests are responsible for hypoxic and hypercapnic events including sleep fragmentation, reduction of slow wave sleep and rapid eye movement sleep. Alertness disturbances and sleep disorders are the most common functional complaints. Memory and cognitive disorders, personality changes and anxiodepressive syndromes may occur but are often neglected due to the increase of frequency with age together with the frequency of SAS; clinicians should consequently be aware of the fact that such troubles may be related to sleep respiratory disorders. In this case polysomnography should be performed before prescribing hypnotics, tranquilizers or sedative antidepressants.