To assess the impact of their child's symptoms of Autism Spectrum Disorder upon parents' anxiety and depression, 68 mothers of boys aged 10 to 15 years (M = 12.6 years, SD = 1.6 years) completed the ASD Behaviour Checklist, the GAD7 and the PHQ9 at a single setting. Results indicated that the boys' restricted and repetitive behaviours had the strongest relationship with their mothers' anxiety and depression, followed by communication difficulties, but the latter set of behaviours did not significantly add to the variance predicted by restricted and repetitive behaviours. Their sons' intense reactions to stressors was the most powerful ASD-related contributor to the anxiety and depression experienced by these mothers. Several suggestions for enhancing parental coping with this aspect of their child's ASD behavioural symptomatology are discussed.