Objective: This study examined measurement variance for Autism Spectrum Disorder (ASD) in the Spence Children's Anxiety Scale - Parent Form (SCAS-P; Spence, 1999). In addition, we developed and evaluated a new parent report measure for anxiety (Macquarie Anxiety Behavioural Scale; MABS). Method: The sample consisted of 734 parents of children aged 3–19 years (i) who were seeking help for their child's anxiety, (ii) who had received a diagnosis of ASD, or (iii) from the community. Results: Evidence for measurement variance of the SCAS-P and MABS was found, revealing different factor structures between the ASD and non-ASD groups. MIMIC modelling showed that the scales performed significantly different across ASD and non-ASD groups. Differential item functioning on a number of the SCAS-P and MABS items was also found. Limitations: This study relied on parent report of symptoms and of community acquired diagnoses of ASD. Conclusion: The MABS is a new parent measure to assess anxiety in children and adolescents and the proposed factor structure produced a reasonably good fit for the data. Similar to the SCAS-P, ASD was found to impact on some of the MABS items indicating that ASD influences parental responding. Eighteen MABS items showed measurement invariance across the anxious and ASD groups and can be considered suitable items for the assessment of anxiety in ASD.