A small number of studies have suggested that, like adults, youth with anxiety disorders experience strikingly elevated rates of sleep problems, particularly insomnia. However, little is known about how insomnia impacts the clinical expression of anxiety disorders or the underlying neural abnormalities implicated in anxiety. This is a critical issue, because if insomnia is found to be a causal or maintaining factor in anxiety, it becomes an important target for the treatment of anxiety. Currently, no studies have examined whether the neural abnormalities exhibited by adults or youth with anxiety are associated with sleep loss. The current study seeks to identify the neural system abnormalities at the core of generalized anxiety disorder (GAD), and examine their relationships with sleep. It employs samples of adolescents with and without GAD, and pairs naturalistic, objective measurement of sleep with functional neuroimaging assessment of the neural circuitry involved in threat reactivity and attentional control.