Introduction: Tourette syndrome (TS) is associated with neuropsychiatric comorbidities, such as Autism Spectrum Disorder (ASD), Attention-Deficit/Hyperactivity Disorder (ADHD), Oppositional Defiant Disorder (ODD) and Obsessive Compulsive Disorder (OCD). They are considered the main source of impairment in TS patients, however family aggregation between TS and other neuropsychiatric disorders has been explored scarcely. We aimed to investigate the association of TS symptoms in probands with other neuropsychiatric symptoms, such as ASD, ADHD and ODD in their siblings and the influence of tic severity, age- or sex-related differences. Methods: The sample of the present study stems from the European Multicenter Tics in Children Study (EMTICS), a longitudinal observational study involving 16 clinical centers, with a subsample of 191 probands and 213 siblings. Severity of motor and vocal tics in probands was assessed using the Yale Global Tic Severity Scale (YGTSS). We also assessed communication problems, restricted and repetitive behaviors with the Autism Spectrum Screening Questionnaire (ASSQ) and the severity of ADHD and ODD symptoms, with the Swanson, Nolan and Pelham-version IV rating scale (SNAP-IV). We used Wilcoxon and Chi-square tests to compare the differences between probands and siblings for continuous and categorical variables, respectively. We analyzed associations between proband’s tic severity and the symptom dimensions in their siblings using generalized linear mixed-effect negative binomial regression models, with a random intercept to account for dependency across the observations from the members of the same family. Results: A higher tic severity in probands was associated with a higher ASSQ total score in their siblings in the fully adjusted model, even after excluding the three items in the ASSQ linked to stereotypies. Moreover, we demonstrated a significant interaction between sex and tic severity upon ODD. Female siblings of probands with higher tic severity had higher inattention and ODD symptoms, whereas no significant effect was found for male siblings. Conclusion: Using a sibling group comparison design model, this multicenter study demonstrated a link between proband’s tic severity and siblings’ neuropsychiatric symptoms. Siblings of children affected with TS showed a higher level of ASD symptoms, whereas ADHD and ODD symptoms were more present in female siblings of probands with a higher severity of tic symptoms.