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Objective: Stress-related sleep reactivity, sleep-related cognitions, and psychological factors play an important role in insomnia. The aim was to investigate their possible association in Insomnia Disorder, insomnia subgroups, and healthy subjects.Methods: The cross-sectional study consisted of 93 subjects who met diagnostic criteria for Insomnia Disorder according to Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5) and of 30 healthy subjects. Survey instruments included the Insomnia Severity Index (ISI), Pittsburgh Sleep Quality Index (PSQI), Ford Insomnia Response to Stress Test (FIRST), Dysfunctional Beliefs about Sleep scale (DBAS), Beck Depression Inventory (BDI), and Zung Self-Rating Anxiety Scale (SAS). Descriptive statistics, Pearson correlations, χ(2)-test, and multiple linear regression were performed.Results: FIRST and SAS best determined the insomnia subjects vs good sleepers (FIRST χ(2) = 109.6, p <0.001, SAS χ(2) = 120.3, p <0.001). FIRST was best predicted by DBAS (p <0.001), PSQI (p <0.001), and SAS by PSQI (p <0.001), ISI (p <0.05), BDI (p <0.001). In the sleep onset subgroup FIRST was related to ISI, PSQI, and DBAS and in the combined subgroup with DBAS. In both subgroups SAS was related to PSQI, ISI, and BDI.Conclusions: Findings suggest potential implications: (1) among the factors that may contribute to insomnia, stress-related sleep reactivity, and psychological factors, such as anxiety symptoms, may distinguish insomnia subjects from good sleepers; (2) sleep reactivity and sleep-related cognitions seem interrelated, unhelpful beliefs may affect the stress reactivity; (3) psychological factors may influence sleep quality and the severity of insomnia; (4) these important sleep-related variables may have similar associations in insomnia subgroups; they may constitute the core factors for insomnia development and maintenance. [ABSTRACT FROM AUTHOR]