Restless legs syndrome (RLS) and attention deficit hyperactivity disorder (ADHD) have consistently been found to coexist frequently. The cause for the relationship of these co-morbid disorders is contradicting, but both disorders are associated with a common dopaminergic dysfunction, low iron status, sleep disruptions and genetic linking. Well-known diagnostic criteria are necessary for early diagnosis and optimal treatment. Further investigation is needed to identify the pathogenesis, the genetic background and better validated treatment options. So far, oral iron treatment can reduce RLS symptoms, while treatment with e.g. central stimulants can reduce ADHD symptoms.