Anxiety disorders are common among adolescents and lead to poor long-term outcomes. Cognitive Behavioural Therapy (CBT) is an evidenced-based intervention for adolescent anxiety disorders, but little is known about whether and how parents should be involved. This systematic review evaluated how parents have been involved and associated treatment outcomes in studies of CBT for adolescent anxiety disorders. Electronic systematic searches were conducted in PsycINFO, Embase, CINAHL, Medline, AMED databases, to identify studies investigating CBT for adolescent anxiety disorder(s) that included parents in treatment. Twenty-three papers were identified. Parents were involved in treatment in a number of different ways: by attending separate parent sessions, joint parent-adolescent sessions, or both, or through provision of a workbook while attending some adolescent sessions. Content varied but was most typically aimed at the parent developing an understanding of core CBT components and skills to help them manage their adolescent's anxiety and avoidance. Treatment outcomes indicate that CBT with parental involvement is an effective intervention for adolescent anxiety disorders; however, it is not possible to draw conclusions regarding whether parental involvement (generally or in any particular form) enhances treatment outcomes. Poor reporting and methodological issues also limit the conclusions. Further research is required to identify whether there are particular types of parental involvement in CBT that bring clinical benefits to adolescents with anxiety disorders generally, as well as in particular circumstances.