Restless legs syndrome (RLS) in the paediatric age is a common disorder and is in many cases associated to attention deficit hyperactivity disorder (ADHD). Yet, it remains ‘the great unknown’ in paediatrics. We do not usually think of it when examining a child with sleep problems, and there is even a tendency to deny its existence in children. ADHD and RLS have common symptoms and frequently share a common aetiopathogenesis (iron deficiency anaemia). Although important progress has been made in recent years in the research conducted on both disorders, further studies must be carried out to examine different treatments or other aspects of RLS in the paediatric population.