The National Institute of Neurological Disorders and Stroke (http://www.ninds.nih.gov/disorders/autism/detail_autism.htm) defines it in this way:
"Autism spectrum disorder (ASD) is a range of complex neurodevelopment disorders, characterized by social impairments, communication difficulties, and restricted, repetitive, and stereotyped patterns of behavior."
The main indicator of autism is impaired social interaction. A person with autism often fails to respond to their name and avoids eye contact. The National Institute of Neurological Disorders and Stroke also describes indicators as: "They have difficulty interpreting what others are thinking or feeling because they can’t understand social cues, such as tone of voice or facial expressions, and don’t watch other people’s faces for clues about appropriate behavior. They may lack empathy." Children with autism are known for showing self-abusive behavior such as head-banging and biting. Children also participate in repetitive behavior such as twirling and rocking back-and-forth.
Early signs of autism are:
Later signs include: