Since a postinfectious or autoimmune etiology is suggested to be involved in the pathogenesis of Tourette's syndrome (TS), we investigated oligoclonal bands (OB) of immunoglobulin G (IgG) in cerebrospinal fluid (CSF), indicating a humoral immune response in the central nervous system. CSF examinations including isoelectric focusing to analyze the presence of OB were performed in 21 TS patients [17 men/4 women, mean age = 29 ± 12 (SD) years]. Isoelectric focusing showed the presence of positive OB in 6, borderline bands in 2, and serum and CSF bands (“mirrored pattern”) in another 2 patients. Clinical data did not correlate with CSF findings. Thus, 38% (8 of 21) of our patients exhibited pathological CSF bands. Since none of them suffered from another disease known to be associated with OB, our results suggest an association with the pathogenesis of TS itself and point to an involvement of immunological mechanisms in TS pathology. © 2010 Movement Disorder Society.