In order to investigate the experience of anxiety and restricted and repetitive behaviours (RRB) in young people with ASD, 19 families with young people with ASD aged between 13 and 20 years completed questionnaire measures of RRB, anxiety, and intolerance of uncertainty. Ten young people also completed a novel semi-structured interview exploring an individualised example of an RRB. Findings demonstrated that young people with ASD can self-report and show insight in to their RRB, and replicated previous findings based on parent report showing a significant positive relationship between RRB and anxiety. This is the first evidence of young person self-report using both quantitative and qualitative data and indicates a range of reasons why young people may engage in RRB.