Anxiety disorders are among the most common comorbid conditions in children and adolescents with autism spectrum disorders (ASDs), although assessment presents unique challenges. Many symptoms of anxiety appear to overlap with common presentations of autism. Furthermore, deficits in language and cognitive functioning make it difficult for such children to convey their emotional states accurately. A comprehensive review of the recent literature was conducted to assay the types and rates of use of tools for evaluating anxiety symptoms in children and adolescents with ASDs. We identified strengths and weaknesses in existing scales, identified instruments that (although imperfect) seem to have a good coverage for youngsters with ASDs, recommended strategies for studying anxiety in these youth, and offered suggestions for future scale development. (Contains 3 tables.)