Cognitive behaviour therapy (CBT) is an efficacious treatment for paediatric anxiety disorders, yet not all children improve following standard treatment protocols. Identifying pre-treatment predictors of poor treatment response is an important area of research to maximise outcomes for children with anxiety disorders. This paper presents a systematic review of pre-treatment predictors of child/adolescent anxiety treatment outcome, including child demographic, child diagnostic and parental factors. Results are based on 47 peer-reviewed articles and 4 dissertations. Results for each predictor are reported according to method of measuring outcome (e.g., endpoint or rate of change). No consistent and clear pre-treatment predictors of paediatric anxiety outcome were identified. Yet, it is worth noting that a number of trends emerged; some significant predictors were identified in more than one study including primary anxiety diagnosis, severity, comorbidity and parental anxiety/psychopathology. With regards to primary anxiety diagnosis, there was emerging evidence that Social Anxiety Disorder predicted poorer treatment response, while GAD predicted better outcome. Greater symptom severity and comorbid externalising symptoms/disorder were also associated with poorer treatment response but not dependably across studies. Some inconsistent evidence also emerged showing that presence of comorbidity, comorbid depression, parental psychopathology, parental anxiety and maternal anxiety were associated with poorer outcomes when outcome was assessed as an endpoint. There were a number of pre-treatment factors that were not related to treatment outcome: age, gender, ethnicity and socio-economic status. Based on a small number of studies, comorbid anxiety, maternal depression, paternal anxiety and paternal depression also failed to predict treatment outcome. Further methodologically strong research is needed to clarify the conclusions made in this review and to investigate a range of predictors considered under preliminary investigation.