Restless Legs Syndrome/Willis Ekbom Disease (RLS/WED) is a common neurological disorder characterized by uncomfortable and unpleasant sensations in the legs, with an urge to move. The symptoms typically begin or worsen during periods of rest, in particular during the evening and at night, while the activity may typically relieve them. The majority of patients complains of poor sleep. Recent studies reported the prevalence is ranging from 5 to 10%. RLS/WED can be divided into primary (patients without associated conditions that may explain the symptoms) and secondary forms (mostly iron deficiency). RLS/WED is typically a chronic condition. The clinical course varies according to the age of onset. A great load of accumulating research and clinical data have led to an extended consensus for a need to enhance the diagnostic criteria. The aim of this paper is to provide a critical comparison among different diagnostic criteria, taking into account respectively the International Classification of Sleep Disorders (ICSD), the International RLS Study Group (IRLSSG) and the Diagnostic and Statistical Manual of Mental Disorders (DSM). There are several remarkable distinctions between the IRLSSG revised criteria, ICSD-3 and DSM-V. Contrary to the DSM-V criteria, ICSD-3 diagnostic criteria are more aligned to the IRLSSG ones. In fact, the five essential criteria of the IRLSSG are also required for the diagnosis of RLS/WED according to ICSD-3. The new IRLSSG criteria provide a more rigorous approach to case ascertainment and a better characterization of patients by specifying clinical significance and course. Future ascertainment of correct diagnosis should include documentation that all five diagnostic criteria are considered.