Signs will typically appear before 3 years old, but....
Difficulty with verbal communication, including problems using and understanding language.
Inability to participate in a conversation, even when the child has the ability to speak.
Difficulty with non-verbal communication, such as gestures and facial expressions.
Difficulty with social interaction, including relating to people and to his or her surroundings.
Inability to make friends and preferring to play alone.
Unusual ways of playing with toys and other objects, such as only lining them up a certain way.
Lack of imagination.
Difficulty adjusting to changes in routine or familiar surroundings, or an unreasonable insistence on following routines in detail.
Repetitive body movements, or patterns of behavior, such as hand flapping, spinning, and head banging.
Preoccupation with unusual objects or parts of objects
at 9:34 AM on Jan. 10, 2011