Majority of the physiological processes in the human organism are rhythmic. The most common are the diurnal changes that repeat roughly every 24 hours, called circadian rhythms. Circadian rhythms disorders have negative influence on human functioning. The aim of this article is to present the current understanding of the circadian rhythms physiological role, with particular emphasis on the circadian rhythm sleep-wake disorders (CRSWD), principles of their diagnosis and chronobiological therapy. The guidelines are based on the review of recommendations from the scientific societies involved in sleep medicine and the clinical experiences of the authors. Researchers participating in the preparation of guidelines were invited by the Polish Sleep Research Society and the Section of Biological Psychiatry of the Polish Psychiatric Association, based on their significant contributions in circadian rhythm research and/or clinical experience in the treatment of such disorders. Finally, the guidelines were adjusted to the questions and comments given by the members of both Societies. CRSWD have a significant negative impact on human health and functioning. Standard methods used to assess CRSWD are sleep diaries and sleep logs, while the actigraphy, when available, should be also used. The most effective methods of CRSWD treatment are melatonin administration and light therapy. Behavioral interventions are also recommended. Afourteen-day period of sleep-wake rhythm assessment in CRSWD enables accurate diagnosis, adequate selection of chronobiological interventions, and planning adequate diurnal timing of their application. This type of assessment is quite easy, low-cost, and provides valuable indications how to adjust the therapeutic approach to the circadian phase of the particular patient.
