AbstractRecent reports established an association of restless legs syndrome (RLS) and spinocerebellar ataxia (SCA) type 1, 2, and 3. To evaluate the contribution of SCA alleles to idiopathic RLS we investigated the CAG repeat length at the SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 loci in 215 patients who fulfilled the clinical criteria of RLS and presented periodic leg movements in sleep (PLMS) in polysomnographic recording. Fifty percent of patients had a positive family history of RLS. We found one intermediate (CAG)43 allele for SCA17 in a 44‐year‐old female with RLS starting at the age of 43. Neurologic examination and family history were unremarkable in this patient. Otherwise, allele distribution did not differ between RLS patients and healthy controls. Stratification for age, age of onset, sex, peripheral neuropathy, and sporadic or familial RLS revealed no effect. Thus, CAG repeat length in the investigated genes is not a major determinant of idiopathic or familial RLS. © 2006 Wiley‐Liss, Inc.