Restless legs syndrome (RLS) occurs as a sensorimotor neurological disorder primarily affecting what the great neurologist Critchely referred to as the pre-dormitum, i.e. state before sleep enabling the entry to sleep. Family history of RLS supports diagnosis of RLS. The failure to respond, at least initially, to dopaminergic treatment, and no indications for leg movements in sleep and in particular no periodic leg movements (PLM) on a sleep study, cast some doubt on diagnosis of RLS. RLS occurs not only as a primary disorder but also secondary to other medical conditions. The RLS occurs secondary to these other conditions, it develops after the other condition has started, gets better or worse in relation to the severity of the other condition, and resolves if the other condition is adequately treated. There are three major secondary causes of RLS.