Circadian rhthym disorders are a broad group of disorders that involve problems with the timing of the internal biologic clock. The two most common disorders are advanced sleep phases syndrome (ASPS) and delayed sleep phase syndrome (DSPS). ASPS occurs when individuals have a tendency to fall asleep early in the evening and wake early in the morning (an advanced sleep phase) as opposed to DSPS, where individuals tend to fall asleep later in the evening and sleep late into the morning. Everyone has a genetically determined preferred sleep phase (i.e. early birds or night owls), however, some individuals have such an extreme tendency that it interferes with their daily functioning. Adolescents tend to be delayed and older individuals tend to be advanced. For more information on ASPS, go to www.sleepeducation.com/Disorder.aspx?id=28 or for DSPS, go to www.sleepeducation.com/Disorder.aspx?id=30 or contact The Sleep Disorders of CDS to find out more about these problems and various treatment options.