Background: The relationship between symptoms of Autism Spectrum Disorder (ASD) and Generalised Anxiety Disorder (GAD) is complex and sometimes confounding. However, exploration of that relationship has significant potential to assist in treatment or avoidance of GAD by identifying ASD-related behaviours as 'targets' for intervention with anxious children as well as for preventative treatments that could be implemented into daily routines before children become anxious. To further understanding of this relationship, the association between parent-ratings of their sons' ASD symptoms and GAD symptoms was investigated in two samples of boys with high-functioning ASD. Methods: Parents of a sample of 90 pre-adolescent (M age = 8.8yr) and 60 adolescent males (M age =14.6yr) completed the Social Responsiveness Scale (SRS) and the GAD subscale of the Child and Adolescent Symptom Inventory (CASI-4 GAD) about their sons. Results: Pre-adolescents had significantly higher SRS scale scores than adolescents. For pre-adolescents, high levels of tension in social situations were associated with 3.5-times greater likelihood of having GAD; for adolescents, experiencing difficulty in changes in routine was associated with a 10-fold increase in risk of GAD. Conclusions: In addition to focussing upon GAD itself, preventative and treatment options aimed at reducing GAD or its risk might profitably recognise and focus upon these two aspects of ASD that are different across the two age groups but each of which was significantly associated with GAD severity and prevalence in this study. (C) 2017 Elsevier Ltd. All rights reserved.