The autistic person may appear aloof and indifferent to those around them. They may be sociable with one person, but unable to function in a group. Communication difficulties include no understanding or use of verbal or non-verbal communication. A common characteristic is an unwillingness to look people in the eye. Impairment of imagination may lead to limited, repetitive play, copying others or problems discerning between fact and fantasy.

A diagnosis of autism must address all three of these areas and there is a whole range (hence the term autism spectrum) of factors and behaviors that can only be evaluated by a number of tests and observations undertaken by medical professionals in different fields including pediatricians and child psychologists.

Frequently occurring features of an autistic person include a state of anxiety, the need for structure and planning, social misunderstandings and difficulty making choices. Autistic children often have a literal understanding of what is said. An underachieving autistic child told by a teacher to pull his socks up is likely to do just that and unwittingly incur the wrath of the adult.