Tourette syndrome (TS) is often accompanied by other symptoms and syndromes. The two best-known co-morbidities are Attention Deficit Hyperactivity Disorder (ADHD) and Obsessive Compulsive Disorder (OCD), but also other conditions like rage-attacks, depression, and sleeping disturbances are frequent in persons with TS. Both in clinical cohorts and in population-based cohorts the prevalence of co-morbidities is high. The presence of co-morbid ADHD and/or OCD has an impact on psychosocial, educational, and neuropsychological consequences of TS and it is associated with higher rates of other co-morbid disorders, like rage, anxiety, and conduct disorders. The symptoms of a co-morbid disorder might appear prior to the time that tics reach clinical attention. The TS phenotype probably changes during the course of the disease. The exact aetiology of the co-occurrence of co-morbid disorders and TS is not known, but they probably all are neurotransmitter disorders. European guidelines recommend first-choice pharmacological treatment, but randomised double-blinded trials are needed. Professionals need to be aware of the close relationship between TS and co-morbidities in order to give the patients the right treatment and support.