The sources of anxiety for a sample of 132 young males with Autism Spectrum Disorder (ASD) were investigated from standardised scales and verbal responses to a series of open-ended questions asked to them and their mothers. As well as using parametric statistics to test for effects on standardised scales, verbal responses were analysed via NVivo to identify nine themes, of which five were most often cited by participants. There were no major age-related differences in the responses from young (aged 6 to 11yr) "vs" older (aged 12 to 18yr) sons or their mothers, but there were differences between mothers' and sons' data. These differences were related to elevated tension and inability to relax by the sons, and were largest for the theme of "unexpected changes" (rated as more anxiety-provoking by the mothers than by their sons) and "specific fears" (rated more anxiety-provoking by the sons than by their mothers). One particular aspect of the sons' Auditory Processing was identified as the sole significant contributor to mother-son disagreement. Implications for clinical processes are discussed.