Autism FAQ-Characteristic Behavior (not all)

Autistic children display unusual behavior. A typical autistic child's behavior is likely to include some of the following:

no speech
non-speech vocalizations
delayed development of speech
echolalia: speech consisting of literally repeating something heard
delayed echolalia: repeating something heard at an earlier time
confusion between the pronouns "I" and "You"
lack of interaction with other children
lack of eye contact
lack of response to people
treating other people as if they were inanimate objects
when picked up, offering no "help" ("feels like lifting a sack of potatoes")
preoccupation with hands
flapping hands
spinning
balancing, e.g. standing on a fence
walking on tiptoes
extreme dislike of certain sounds
extreme dislike of touching certain textures
dislike of being touched
either extremely passive behavior or extremely nervous, active behavior
extreme dislike of certain foods
behavior that is aggressive to others
lack of interest in toys
desire to follow set patterns of behavior/interaction
desire to keep objects in a certain physical pattern
repetitive behavior (perserveration)
self-injurious behavior
"islets of competence", areas where the child has normal or even advanced competence. Typical examples:
drawing skill
musical skill
arithmetic
calendar arithmetic
memory skills
perfect pitch

There are other conditions which sometimes coincide with autism:
synesthesia(an unexpected sensation arises when a particular sense modality is stimulated)
Cerebellar abnormalities revealed by MRI scans
raised levels of serotonin in the brain
hypotonia
sensory integration disorder
generalized anxiety disorder