A frequent clinical observation is that patients with insomnia strive to control their sleep. However, sleep is an involuntary physiological process, which cannot be placed under full voluntary control. Therefore, direct, voluntary attempts to control sleep may actually exacerbate and perpetuate insomnia. To date, no reliable scale has been available to test this hypothesis directly. Moreover, while sleep effort is a core International Classification of Sleep Disorders--Revised criterion for psychophysiological insomnia, clinicians lack a reliable measure with which to assess the construct. In this initial scale validation study, we present psychometric data for the Glasgow Sleep Effort Scale based on a relatively small but representative sample of patients with insomnia and good sleepers. The clinical and research value of the new scale is discussed and future research directions are described.