Clinical sleep medicine has developed rapidly in the last two decades. Especially the diagnosis and differential‐diagnosis of different subtypes of insomnia is much more sophisticated now than it was 20 years ago.

Restless legs syndrome (RLS) is a common, though often underdiagnosed, disorder with high impact on sleep. It is also called "the most common disorder you never heard of". Though already described in detail in 1945 by Ekbom (Ekbom 1945), diagnosis criteria were set up a half‐century later by the International Restless Legs Syndrome Study Group (IRLSSG, Walters 1995). The diagnostic criteria have been revised at a consensus conference held at the National Institute of Health (Allen 2003).

Essential criteria for the diagnosis of the disorder are:

• An urge to move the legs accompanied or caused by uncomfortable and unpleasant sensations in the legs.

• The urge to move or unpleasant sensations begin during periods of rest or inactivity such as lying or sitting.

• The urge to move or unpleasant sensations are relieved or partially relieved by movements such as walking, stretching etc.

• The unpleasant sensations and the urge to move only occur in the evening or at night.

Supportive, not mandatory features of the syndrome are periodic leg movements during awake (PLMW) and during sleep (PLMS). The quantification of PLMS is routinely performed in the sleep laboratory by the recording of bilateral surface electromyogram of anterior tibial muscles. PLMS also occur frequently in several other sleep disorders and may also be pres‐ent in subjects without any complaints of sleep disturbance. This applies especially to the elderly, albeit not as frequently as in patients with RLS (Allen 2003, for overview see also Hornyak 2004). Although the presence of PLMS is not specific to RLS, an elevated PLMS index (> 5 PLMS per hour of sleep) is supportive of the diagnosis of RLS (Allen 2003). The family history for the disorder is positive in 40‐60% of cases, suggesting a genetic predisposition in this group. Clinically, patients with a positive family history have an earlier onset of symptoms (before age 45) than patients without relatives afflicted with RLS. A positive response to L‐dopa also supports the diagnosis of RLS as an estimated 90% of patients report some symptom relief when treated with this agent. However, studies investigating the specifity and validity of this response have not yet been published.

Sleep disturbances are a common associated feature of the disorder and are usually the reason why patients seek medical advice (Hening 2004a). Sleep disturbances are also considered to be characteristic of the full expression of the disorder. However, because of the frequent occurrence of sleep problems in other disorders and their limited occurrence in patients with milder RLS, they are not considered as necessary for or even supportive of the diagnosis of RLS (Allen 2003). The natural course of the disorder varies greatly for milder RLS. For the patients whose symptoms start in young adult life and who eventually seek treatment, the severity and frequency of symptoms typically increases over time. Thus, the disorder is generally considered to be a chronic condition. The physical examination is usually negative for patients with idiopathic (primary) RLS. However, it is important for the clinician to look for factors that may exacerbate or trigger symptoms (secondary RLS). Aside from the established causes of secondary RLS (e.g. end‐stage renal disease, preg‐nancy and iron deficiency), there are no known physical abnormalities associated with the disorder.

Epidemiological surveys in West Europe and in the USA indicate that up to 10% of the population are afflicted with RLS. The prevalence increases with age and is in females twice as high as in males (Phillips 2000; Rothdach 2000; Ulfberg 2001; Högl 2003; Berger 2004). According to a recent survey, one third of the persons reporting RLS symptoms (i. e. 2‐3% of the population) may need medical treatment (Hening 2004a).

The condition was treated earlier with clonazepam, a benzodiazepine. In the meantime, the mainstream of therapy focuses on the therapy with L‐dopa and dopamine agonists (for a recent overview of the literature see Happe 2004; Hening 2004b). Alternative treatment options are antiepileptics like gabapentine, valproic acid and opioids (Walters 1993; Garcia‐B 2002; Eisensehr 2004; for overview see Hening 1999; Silber 2004). Though some of these substances are meanwhile used often in the treatment of RLS (e.g. opioids), the number of studies looking into substances other than dopaminergic drugs is still limited.

The etiopathophysiology of the disorder has not yet been understood. A possible dysfunction of the central nervous dopaminergic system has been generally accepted (Hening 2004; Trenkwalder 2004). An involvement of the dopaminergic system is also being assumed due to the effect that dopaminergic drugs have on the disorder (see a descriptive review of Hening 2004b). As the pathophysiology of the disorder is still unknown, there is no curative treatment for it. The treatment of RLS thus remains symptomatic.

The aim of the present review is to evaluate the therapeutic efficacy of L‐dopa treatment for the restless legs syndrome. Pharmacological treatment aims to suppress the nocturnal urge to move and the unpleasant sensations. These entail in many cases a severe curtailment of sleep and subsequently daytime fatigue, tiredness and impaired functioning. Furthermore, it is our aim to evaluate whether L‐dopa treatment suppresses periodic leg movements during sleep, which is up to now the only objective marker of the disorder. PLMS are not a pathognomonic feature of RLS as they occur also in other disorders. Therefore, PLMS can only be considered as a secondary outcome measure. Further secondary outcomes of our meta‐analysis such as parameters of daytime functioning, if studied yet, will be included.