<![CDATA[Delayed sleep phase disorder (DSPD) is a circadian rhythm sleep-wake disorder characterized by a persistent delay of the major sleep period relative to socially desired sleep and wake times. DSM-5 classifies it as delayed sleep phase type (307.45; G47.21), and the International Classification of Sleep Disorders lists it as a distinct entity. DSPD is the most frequent circadian disorder, accounting for about 83% of cases, with a prevalence of 0.17% in the general population, 1% to 16% among adolescents and young adults, and 6.7% to 16% among patients attending sleep clinics for insomnia. Its etiology is multifactorial, comprising a phase delay of circadian markers, a longer intrinsic circadian period, an abnormal phase angle of entrainment, slower accumulation of homeostatic sleep drive, and altered responsiveness to photic zeitgebers, together with genetic vulnerability and behavioral, cognitive, and emotional factors. Patients present with chronic sleep-onset insomnia when sleep is attempted at conventional hours, difficulty awakening, and excessive daytime sleepiness, whereas sleep quality is essentially normal when they follow their own schedule. Diagnosis is clinical and is supported by a prospective sleep diary, actigraphy, and circadian phase markers such as dim light melatonin onset. Management is multimodal, comprising sleep hygiene education, chronotherapy, timed morning bright light with avoidance of evening light, and exogenous melatonin, which advances endogenous melatonin onset and sleep onset and shortens sleep-onset latency. Prognosis depends on adherence and psychiatric comorbidity; early detection and management of comorbidity are essential to prevent academic, occupational, and psychosocial impairment.]]>
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