Restless legs syndrome (RLS) is a sensory-motor disorder characterized by discomfort of and urge to move the legs, primarily during rest or inactivity, partial or total relief with movement, with presence or worsening exclusively in the evening. It is a relatively common but frequently unrecognized disorder, with a prevalence ranging from 2.5 to 15% of the general population, increasing with age and with a female preponderance. The diagnosis is clinical but polysomnography is useful to determine its profound impact on sleep (difficulties in sleep onset, maintaining sleep during the night, and sleep fragmentation) and for the evidence of periodic legs movements during sleep and wake. RLS is generally idiopathic, with familial association in 40-60% of the cases, but may also be symptomatic of such associated conditions (secondary forms) as peripheral neuropathies, uremia, iron deficiency (with or without anemia), diabetes, Parkinson's disease and pregnancy. Response to dopaminergic drugs indicates that dopamine receptors are implicated, and although much progress has been made in diagnosis and treatment in the last decade, more is needed for complete elucidation of the etiology and pathophysiology of RLS.