Because autism is not understood by science, and there is no blood test or brain imaging pattern that can result in a diagnosis, autism is diagnosed by a constellation of symptoms. The following are symptoms that are frequently seen in autism, focused on the triad of symptoms that are said to scientifically characterize autism (the actual DSM-IV criteria physicians use for diagnosis are listed at the bottom of this sub-page).

Social Skills

• Fails to respond to his or her name
• Has poor eye contact
• Appears not to hear you at times
• Resists cuddling and holding
• Appears unaware of others' feelings
• Seems to prefer playing alone — retreats into his or her "own world"

Language

• Starts talking later than other children
• Loses previously acquired ability to say words or sentences
• Does not make eye contact when making requests
• Speaks with an abnormal tone or rhythm — may use a singsong voice or robot-like speech
• Can't start a conversation or keep one going
• May repeat words or phrases verbatim, but doesn't understand how to use them

Behavior

• Performs repetitive movements, such as rocking, spinning or hand-flapping
• Develops specific routines or rituals
• Becomes disturbed at the slightest change in routines or rituals
• Moves constantly
• May be fascinated by parts of an object, such as the spinning wheels of a toy car
• May be unusually sensitive to light, sound and touch and yet oblivious to pain

In addition, there are numerous autistic symptoms which are not addressed in these criteria and which are not recognized by most scientists are being core to the condition. However, parents tend to be very aware of these behaviors as core to autism.

-  Sensory Processing Abnormalities: Any parent or occupational therapist will tell you that autistic children almost universally have sensory processing abnormalities, typically what is called sensory defensiveness. Sensory defensiveness involves an overreaction of the child's nervous system to the sensory world around them. The auditory and tactile senses seem to be most often involved. Children with sensory defensiveness experience nervous systems that fail to habituate (learn to ignore) sensory information that the average person can't even perceive because their nervous system is performing correctly, like tags in shirts, the texture of certain foods, the dripping of a faucet, or the humming of the refrigerator condensor. This is a core, not tangential, characteristic of autism that results in many other aspects of the disorder.

- Withdrawal as a Coping Strategy: This symptom is touched upon above in the specific symptoms. However, withdrawal is a pervasive characteristic of autism. For the autistic individual, the world is a profoundly stressful place. The simplest and most direct way of coping with such a world is to withdraw away from it. And, autistic children are experts at this. They may fail to engage in conversation or just stop interacting voluntarily with people in their world, or they may stop playing with other children, or spend most of their time in their room away from the stressors in their world. If the world becomes too much for them, they may simply go catatonic for periods of time, shutting down their sensory channels to buffer them from a world they don't have the capacity to deal with at that moment.

-  Associational Learning:  Another common autistic symptom is an increased number of negative associations. According to My Theory, their excessively excitatory nervous systems allow for the abnormally easy creation of synaptic associations. What this means is that if an autistic child walks into a room, and his mom is using the vacuum cleaner that the defensive child hates, there is a much greater chance than in normal people that his brain will create an association between the neutral room and the hated machine, which causes the child to resist entering that room again even if the vacuum cleaner is no longer present.

- Anxiety:  Anxiety is also an almost universal autistic symptom. Autistic children nearly all have some level of diagnosable anxiety disorder. Also, they just appear anxious most of the time. The world stresses them out, and they respond with symptoms of anxiety, such as nervous rocking, withdrawal, and obsession with order and routine.

- Melt Downs:  One other symptom that nearly every parent of an autistic child knows well is the melt down. Autistic children only have a limited capacity to deal with stress in their world, and things that stress them out may be completely unrecognizable to the average person, like their parent driving the wrong route home, or the ice cream being chocolate chip instead of chocolate chip mint. The stress they experience is disproportionate to the stress a normal person would experience from the same exposure. And, when the child's ability to cope has ended, when the child's reservoir for additional stress is overflowing, the melt down is almost an inevitable consequence. The form of melt down varies from child to child and from time to time, but may involve symptoms from catatonia to a 30 minute screaming fit. There is typically little that can be done about the melt down, once it has occurred, other than let it run its course and try to prevent the next one.

DSM-IVR DIAGNOSTIC CRITERIA

In the United States, The Diagnostic and Statistical Maual, Version IV-R is the tool used by doctors in America to diagnose psychological disorders. It uses the following criteria to diagnose autism:

A.  A total of six (or more) items from (1), (2), and (3), with at least two from (1), and one each from (2) and (3):

1. qualitative impairment in social interaction, as manifested by at least two of the following:
   1. marked impairment in the use of multiple nonverbal behaviors such as eye-to-eye gaze, facial expression, body postures, and gestures to regulate social interaction
   2. failure to develop peer relationships appropriate to developmental level
   3. a lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest)
   4. lack of social or emotional reciprocity
2. qualitative impairments in communication as manifested by at least one of the following:
   1. delay in, or total lack of, the development of spoken language (not accompanied by an attempt to compensate through alternative modes of communication such as gesture or mime)
   2. in individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others
   3. stereotyped and repetitive use of language or idiosyncratic language
   4. lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level
3. restricted repetitive and stereotyped patterns of behavior, interests, and activities, as manifested by at least one of the following:
   1. encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus
   2. apparently inflexible adherence to specific, nonfunctional routines or rituals
   3. stereotyped and repetitive motor manners (e.g., hand or finger flapping or twisting, or complex whole-body movements)
   4. persistent preoccupation with parts of object.

B.  Delays or abnormal functioning in at least one of the following areas, with onset prior to age 3 years: (1) social interaction, (2) language as used in social communication, or (3) symbolic or imaginative play.