Activated glial cells play an important role in a variety of neurological disorders. This study examines S100B protein levels in the serum of patients with Gilles de la Tourette syndrome, as potential marker for glial cell function. Two groups of children were examined: 61 reference patients and 33 patients with Gilles de la Tourette syndrome. It was found that S100B serum concentrations in the reference group decrease with increasing age. Furthermore it was found that the mean S100B concentration in serum of children with Gilles de la Tourette syndrome is significantly higher than in the reference group. These preliminary results suggest that glial tissue might be involved in the pathophysiology of the syndrome.