Delayed sleep-phase syndrome (DSPS), also known as delayed sleep-phase disorder (DSPD) or delayed sleep-phase type (DSPT), is a circadian rhythm sleep disorder, a chronic disorder of the timing of sleep, peak period of alertness, hormonal and other rhythms. People with DSPS tend to fall asleep well after midnight and also have difficulty waking up in the morning.

Often, people with the disorder report that they cannot sleep until early morning, but they fall asleep at about the same time every "night", no matter what time they go to bed. Unless they have another sleep disorder such as sleep apnea in addition to DSPS, patients can sleep well, and have a normal need for sleep. Therefore, they find it very difficult to wake up in time for a typical school or work day since they have only slept for a few hours. However, they sleep soundly, wake up spontaneously, and do not feel sleepy again until their next "night" if they are allowed to follow their own maladjusted schedule, e.g. sleeping from 4 a.m. to noon.

The syndrome usually develops in early childhood or adolescence, Dagan Y; Eisenstein M Circadian rhythm sleep disorders: toward a more precise definition and diagnosis. Chronobiol Int 1999 Mar;16(2):213-22 and sometimes disappears in adolescence or early adulthood. It can be to a greater or lesser degree treatable, but cannot be cured. A reported 200,000 teenagers in the United States and Canada suffer from the disorder.

DSPS was first formally described in 1981 by Dr. Elliot D. Weitzman and others at Montefiore Medical Center. * It is responsible for 7 -10% of cases where patients complain of chronic insomnia. However, as few doctors are aware of its existence, it often goes untreated or is treated inappropriately. DSPS is frequently misdiagnosed as primary insomnia or as a psychiatric condition.