Restless legs syndrome (RLS) is a sensorimotor disorder characterised by a complaint of an almost irresistible urge to move the legs. RLS is diagnosed clinically by means of the four essential criteria of the International Restless Legs Syndrome Study Group. In doubtful cases, neurophysiological examinations, such as polysomnography and/or a suggested immobilisation test, can be performed to confirm a clinical suspicion of RLS. Several other conditions may present sensorimotor complaints with features similar to RLS; a careful sleep history is required to avoid a misdiagnosis. Three different scales have been validated to assess the severity of RLS. In the general population, RLS prevalence ranges from 0.1% to 11.5%, with a high number of patients affected by a primary form of the sleep disturbance (70%-80%). However, several clinical conditions have been associated with RLS, such as iron deficiency, uraemia, pregnancy and polyneuropathy. Furthermore, recent studies show that RLS may be associated also to type 2 diabetes mellitus and to multiple sclerosis. RLS has a negative impact on sleep, cognitive functions, quality of life and mental status. Higher awareness of RLS among physicians is required; it remains an underdiagnosed clinical condition.