Restless legs syndrome (RLS) is a frequent sleep-related movement disorder with disturbed sleep and quality of life. RLS patients complain about increased daytime sleepiness, but there are only few and inconsistent reports about cognitive functioning in this group. We compared cognitive performance of 23 unmedicated RLS patients to that of 23 healthy controls matched individually for age, gender, and educational level. Cognitive tasks were chosen to assess short-term attention, working memory, learning and memory, verbal fluency, and executive functioning. RLS patients performed worse than controls in the area of attention and verbal fluency, and performance in these tasks was associated with RLS severity, sleep quality, depression scores, and memory. There was no difference for working memory, memory, learning, cognitive flexibility, and abstract reasoning. We conclude that there is evidence for deficits in short-term attention and verbal fluency in RLS patients. © 2010 Movement Disorder Society.