Background: Unhelpful sleep related cognitions play an important role in insomnia and major depressive disorder, but their role in seasonal affective disorder has not yet been explored. Therefore, the purpose of this study was to determine if individuals with seasonal affective disorder (SAD) have sleep related cognitions similar to those with primary insomnia, and those with insomnia related to comorbid nonseasonal depression. Methods: Participants (n=147) completed the Dysfunctional Beliefs and Attitudes about Sleep 16 item scale (DBAS-16) and the Structured Interview Guide for the Hamilton Depression Rating Scale, Seasonal Affective Disorder Version (SIGH SAD), which assesses self reported sleep problems including early, middle, or late insomnia, and hypersomnia in the previous week. All participants were assessed in winter, and during an episode for those with a depressive disorder. Results: Individuals with SAD were more likely to report hypersomnia on the SIGH SAD. as well as a combined presentation of hypersomnia and insomnia on the Pittsburgh Sleep Quality Index (PSQI). The SAD group reported DBAS-16 scores in the range associated with clinical sleep disturbance, and DBAS-16 scores were most strongly associated with reports of early insomnia, suggesting circadian misalignment. Limitations: Limitations include the self-report nature of the SIGH-SAD instrument on which insomnia and hypersomnia reports were based. Conclusions: Future work could employ sleep- or chronobiological-focused interventions to improve clinical response in SAD. (C) 2013 Elsevier B.V. All rights reserved