Introduction Gilles de la Tourette syndrome (GTS) is a childhood-onset neuropsychiatric disorder characterised by multiple tics and often associated with behavioural problems. Although there is evidence of significantly reduced self-esteem in children and adolescents with GTS, little is known about perceived self-concept and its clinical determinants at the transition age between adolescence and adulthood. We therefore set out to investigate self-concept in a clinical sample of young patients with GTS at this crucial age for personal development. Methods In addition to standard demographic and clinical data, we collected self-ratings using a standardised battery of psychometric instruments, as well as the Multidimensional Self Concept Scale, a comprehensive questionnaire developed to assess self-concept in subjects aged 9– to 19 years, tapping into the social, competence, affect, academic, family, and physical domains. Results We found that patients diagnosed with at least one co-morbid psychiatric disorder (“GTS-plus” phenotype) reported significantly lower self-concept than patients with “pure GTS”, whereas tic-related variables had no impact on self-concept. Anxiety symptoms were the main determinants of self-concept, especially trait anxiety with regard to social and affective domains. Affective symptoms could also have a negative impact on the physical, affective, competence, and social domains of self-concept. Conclusion Routine screening for anxiety and affective symptoms should be recommended in all patients with GTS seen at transition clinics from paediatric to adult care, in order to implement effective treatment interventions whenever possible.