Anxiety and specific anxiety disorders are very common in people on the autism spectrum. For example, according to a research review conducted by van Steensel, Bögels and Perrin (2011)
“The results reveal substantial comorbidity for anxiety in children and adolescents with an autistic spectrum disorder: nearly 40 percent were estimated to have clinically elevated levels of anxiety or at least one anxiety disorder…
“In the present study, specific phobia was most common at nearly 30%, followed by obsessive-compulsive disorder in 17%, social anxiety disorder and agoraphobia in nearly 17%, generalized anxiety disorder in 15%, separation anxiety disorder in nearly 9%, and panic disorder in nearly 2%. By way of comparison, anxiety disorders in typically developing children are estimated to occur in 2.2-27%...
“In addition, with the exception of panic disorder, the rates of the specific anxiety disorders observed in children with an autistic spectrum disorder are more than two times higher than in typically developing children … and higher than found in children seeking treatment for ADHD ... and learning difficulties.”
However, Grondhuis and Aman (2012) noted that it is very difficult to be sure of the actual prevalence rate of anxiety in children (and therefore adults) on the autism spectrum for a number of reasons. These include the lack of appropriate tools to measure anxiety in autistic children, symptom overlap between the two conditions (such as social avoidance, rigidity, and repetitive behaviors) and the fact that poor language and cognitive skills make it difficult for some children to convey their emotional states accurately.