Individuals with autism spectrum disorder (ASD) are at a higher risk for developing co-occurring anxiety symptoms and diagnosable anxiety disorders compared to children with neurotypical development (NTD). The objective of the current study was to characterize the prevalence and phenomenology of anxiety in preschool-aged children with ASD. Our sample consisted of preschoolers (M = 52.8 months, SD = 10.8 months) with ASD (n = 77, 66% with co-occurring intellectual disability, ID) and NTD (n = 55). We employed multi-method (questionnaire and semi-structured diagnostic interview) and multi-informant (parent- and teacher-report) assessments of anxiety. Children with ASD were significantly more likely to meet criteria for an anxiety disorder than children with NTD. Over 70% of our sample with ASD met DSM-5 criteria for an anxiety disorder, with Specific Phobia and Separation Anxiety Disorder being the most prevalent. A range of specific fears was endorsed in the group with ASD, many of which overlapped with ASD symptoms. Parents, but not teachers, also reported greater anxiety symptoms for children with ASD relative to the comparison sample. Prevalence and phenomenology of anxiety in our sample with ASD generally did not differ between those with and without co-occurring ID, with the exception of higher rates of generalized anxiety in those without ID. Results showed poor concordance between parent questionnaires and a semi-structured diagnostic interview in detecting clinically-elevated anxiety in children with ASD. Implications for clinical practice and research are discussed.