Anxiety in children with autism spectrum disorder (ASD) negatively affects their social interactions, and quality of life. It is necessary to identify early risk factors for anxiety to tailor prevention and interventions. We aimed to examine the clinical level of anxiety in children with ASD from 5 to 10�years of age and identify potential early risk factors 3�years earlier. Participants were ASD children included in ELENA, a French prospective cohort. In this study, we used the collection of data at Time 1-T1 (at baseline) and Time 2-T2 (3�years after T1). Two groups were identified at T2 according to the threshold for anxiety on the CBCL: ASD-only group and ASD + anxiety group. Our results showed that half of the children in our sample had a clinical level of anxiety at T2. Regression analysis showed that greater ASD severity and lower sensory processing difficulties predicted lower anxiety, whereas higher levels of restricted and repetitive behaviours tended to predict higher levels of anxiety. The high prevalence of clinical-level anxiety in our sample suggests the need for specific assessment and targeted treatment of anxiety on a routine basis.