Clinical and genetic observations of Gilles de la Tourette syndrome were carried out on members of 14 families from the Minneapolis area. An unusual number of the families were of Jewish and other Eastern European ancestry, and in all but one of these families multiple members were affected. These observations parallel our earlier findings based on 21 families from the New York City area. Together with recent evidence indicating relative instability of a specific enzyme in some patients, these observations suggest that there is a genetically determined form of Gilles de la Tourette syndrome.