Definition Restless legs syndrome (RLS) is a major cause of comorbid insomnia. It is characterized by four basic symptoms: an urge to move the legs, usually accompanied by unpleasant sensations; worsening of symptoms by rest; relief of symptoms by activity; and worsening of symptoms in the evening or night (1,2). The unpleasant sensations are typically described as creepy-crawly or worm-like, but patients use varied descriptors and not uncommonly find it hard to label the quality of the discomfort. A minority will describe the sensations as painful and some will experience only the need to move without associated sensations. Usually the symptoms are experienced bilaterally, but one limb may predominate, with discomfort sometimes alternating between different sides. In some patients the symptoms may also be experienced in other areas of the body, especially the arms (3). The urge to move is precipitated by physical rest such as sitting or lying down and may be especially severe in prolonged situations of enforced quiescence, such as traveling in a car or plane or sitting in a theater. Reduced alertness may enhance the severity of RLS and, conversely, stimulating mental activities may help alleviate the discomfort. Activities such as walking, stretching or bicycling result in relief but symptoms recommence after the activity is discontinued. Soaking or massaging the affected limb may also provide temporary relief. The characteristic circadian rhythmicity of RLS results in symptoms frequently being most severe in bed, either before sleep onset or on waking during the night.