Three main factors, hyperarousal, circadian dysrhythmia, and homeostatic dysregulation, are thought to underlie chronic insomnia. To date, most of the empirical work has focused on the issue of hyperarousal and very little work has been undertaken on the issue of sleep homeostasis. In the present paper, we review the five lines of evidence which may be used to support the proposition that sleep homeostasis is altered in Primary Insomnia. These include findings pertaining to Slow Wave Sleep density, level of daytime sleepiness, sleepiness following sleep deprivation, recovery sleep following sleep deprivation, and response to sleep restriction therapy. In addition, we provide a discussion regarding how hyperarousal and circadian factors may interact with altered sleep homeostasis, and suggestions for further inquiry.