Tourette syndrome (TS) is a chronic, neurobiological disease, characterized by the presence of motor and vocal tics and it is often accompanied by associated symptoms. The two best-known co-morbidities are Obsessive-Compulsive Disorder (OCD) and Attention Deficit Hyperactivity Disorder (ADHD). The fact that TS aggregates strongly in families suggests that family members share either genetic and/or environmental risk factors contributing to TS. Numerous studies have been performed to examine the familiality in TS, but clear-cut factors to predict hereditability in TS have not been found yet. We have examined a large Danish clinical cohort of children with TS (N=307). Validated diagnostic instruments were used to assess the presence of co-morbidities in the children with TS. A three-generation pedigree was drawn for all the probands and through reports from the family, a family history and the frequency of affected relatives was noted. The rates of tics, symptoms of OCD, and ADHD among relatives are similar to the rates found in other countries and are higher than in the general population. Although the role of sex in determining the phenotype has to be examined more thoroughly, we found that male relatives were more likely to have tics and female relatives were more likely to have symptoms of OCD. When comparing the relatives to male patients with relatives to female patients, there were no differences in the rates of symptoms, apart from symptoms of ADHD that were more frequent in second-degree relatives to female patients. The severity of tics and the presence of co-morbidity did not seem to predict the familiality of TS and its associated symptoms.