Stereotypic movement disorder. Motor stereotypies are among the diagnostic charac-
teristics of autism spectrum disorder, so an additional diagnosis of stereotypic movement
disorder is not given when such repetitive be haviors are better explained by the presence
of autism spectrum disorder. However, when stereotypies cause self-injury and become a
focus of treatment, both diagnoses may be appropriate.
Attention-deficit/hyperactivity disorder. Abnormalities of attention (overly focused or
easily distracted) are common in individuals with autism spectrum disorder, as is hy-
peractivity. A diagnosi s of attention-deficit/hyperactivity disord er (ADHD) should be
considered when attentional difficulties or hyperactivity exceeds that typically seen in in-
dividuals of comparable mental age.
Schizophrenia. Schizophrenia with childhood onset usually develops after a period of
normal, or near normal, development. A prod romal state has been described in which so-
cial impairment and atypical interests and belie fs occur, which could be confused with the
social deficits seen in autism spectrum d isorder. Hallucinations and delusions, which are
defining features of schizophrenia, are not features of autism spectrum disorder. How-
ever, clinicians must take into account the potential for individual s with autism spectrum
disorder to be concrete in their interpretati on of questions regarding the key features of
schizophrenia (e.g., “Do you he ar voices when no one is th ere?” ”Yes [on the radio]”).
Comorbidity
Autism spectrum disorder is frequently assoc iated with intellectual impairment and struc-
tural language disorder (i.e., an inability to  comprehend and construc t sentences with proper
grammar), which should be noted under the relevant specifiers when applicable. Many in-