BACKGROUND: Repetitive thought is a hallmark of several psychopathological conditions and in particular a perpetuating and maintaining factor in Insomnia Disorder. Accordingly, one of the primary complaints reported by Insomnia patients is the inability to shut-off or control thoughts. Worry and rumination are the two best-known styles of repetitive thought leading to sleep disturbances. The aim of this study was to investigate the relationship of these two cognitive processes on nocturnal sleep indices objectively recorded by polysomnography. METHODS: 27 Insomnia patients and 20 healthy controls matched for sex and age were recruited and completed a comprehensive assessment aimed to evaluate sleep quality, excessive daytime sleepiness, insomnia severity, worry, rumination, depressive and anxious symptomatology, and the ability to produce reasonable cognitive estimates. Sleep diaries indices and polysomnographic recordings were evaluated. RESULTS: Insomnia patients showed increased levels of worry and rumination in comparison to controls. Our polysomnographic study revealed that these two different types of repetitive thoughts were significantly associated with objective sleep variables. In particular, heightened worry levels were related to an augmented wake after sleep onset and diminished total sleep time, sleep efficiency and percentage of REM sleep, whereas rumination was associated with an increase of sleep latency and a decrement of sleep efficiency. However, after controlling for anxiety and depressive symptoms only worry maintained a significant relationship with polysomnographic variables. Remarkably, repetitive thoughts did not correlate with microstructural REM sleep features and quantitative EEG analysis. CONCLUSION: Our study indicates the existence of a significant relationship between daytime levels of repetitive thought and sleep, thus corroborating the hypothesis of an interplay between cognitive and nocturnal electrophysiological activity in insomniacs. Copyright © 2017 Elsevier B.V. All rights reserved.