Background: Reports of subjective sleep impairments have been replicated in adults with bipolar disorder (BD) and young BD patients. Furthermore, circadian rhythm alterations are a core feature of BD. Despite the impairment in circadian rhythms and altered sleep included in various heuristic developmental models of BD, thus far, biomarkers in population at risk for BD have not been sufficiently objectively validated. Thus, we conducted: a) Explorative study of sleep and rest-activity circadian rhythm among offspring of BD parents. b) Study of sleep and rest-activity circadian rhythm among offspring of BD parents without the presence of psychopathology (except depression and anxiety disorders) based on our exploratory findings. Methods: a) 14 days of actigraphic assessment and subjective scales (Pediatric Sleep Questionnaire, PSQ; the Morningness/Eveningness Questionnaire, MEQ; and The General Behavior Inventory Sleep Subscale, GBISS) to assess circadian preference, and to identify sleep impairment symptoms. Psychopathology was assessed using psychiatric interview. b) ≥ 14 days of actigraphic assessment with advanced methods to assess the chronotype, social jet lag and sleep macrostructure, psychiatric interview and subjective psychometric scales to assess the full psychopathology profile. Results:..