Autistic children experience higher levels of anxiety than their peers. Making appropriate diagnoses of anxiety disorders and providing effective treatment for these children is particularly difficult. Inconsistent evidence suggests that levels of anxiety in autistic children are related to intellectual functioning. We provide the first meta-analysis of this evidence. A systematic search identified 49 papers for review. These papers included measures of anxiety and intelligence quotient in 18,430 autistic children. Studies employing correlations showed evidence of a significant relationship between intelligence quotient and anxiety in autistic children: children with higher intelligence quotient scored higher on measures of anxiety. Studies directly comparing groups of autistic children with and without intellectual disability also supported this conclusion. Most studies employing other designs also supported this finding. Employing a quality assessment framework identified common threats to validity. Many studies used measures of anxiety that were not validated across the samples they measure. This was most notable for those autistic children with an intellectual disability. It is vital that future research determines whether the identified relationship between intelligence quotient and anxiety reflects something important in the mechanism for anxiety in autistic children, or quantifies the lack of sensitivity of our measures of anxiety across different groups.