Sleep laboratory and epidemiological studies indicate that insomnia is a frequent finding in patients with psychiatric disorders. In this respect, insomnia associated with a major depression or an anxiety disorder, mainly generalized anxiety disorder (GAD), is the most prevalent diagnosis. According to available evidence, the sleep disturbance associated with mild-to-moderate GAD is a sleep-maintenance insomnia, and to a lesser extent a sleep-onset insomnia. Insomnia associated with mild-to-moderate GAD generally responds to psychological treatments and anxiolytic benzodiazepines. Moreover, concomitant administration of hypnotic medication can be contemplated in patients with severe GAD.