Incidence
10 - 15 per 10,000 children are autistic and an additional 12 - 20 per 10,000 have autistic-like features. Three boys to one girl have the disorder.

Diagnosis
The DSM-IV-TR (2000) has identified Autistic Disorder as one disorder under the wider category of Pervasive Developmental Disorders. Under the broader category there are other disorders included such as Asperger's Syndrome, Rett's Disorder, Childhood Disintegrative Disorder, and Pervasive Developmental Disorder (Not Otherwise Specified). DSM-IV-TR has identified the following diagnostic criteria for the Autistic Disorder.

1. 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 interactions, as manifested by at least two of the following:
      1. marked impairment in the use of multiple nonverbal behaviours such as eye-to-eye gaze, facial expression, body postures, and gestures to regulate social interaction
      2. failure to develop peer relationships appropriate to develop mental level
      3. a lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g. by lack of showing, bringing, or pointing out objects of interest)
      4. lack of social or emotional reciprocity
   2. qualitative impairment in communication as manifested by at least one of the following:
      1. delay in, or total lack of, the development of spoken lan guage (not accompanied by an attempt to compensate through alter native modes of communication such as gestures and 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 ppropriate to developmental level
   3. restricted repetitive and stereotyped patterns of behaviour, 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 isabnormal either in intensity or focus
      2. apparently inflexible adherence to specific, nonfunctional routines or rituals
      3. stereotyped and repetitive motor mannerisms (e.g. hand or finger flap ping or twisting, or complex whole-body movements)
      4. persistent preoccupation with parts of objects
2. 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
3. The disturbance is not better accounted for by Rett's Disorder or Childhood Distintegrative Disorder. American Psychiatric Association (2000). Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision (DSM-IV-TR) (p. 79).Washington, D.C.: American Psychiatric Association.
   
   It is still not clear what precise deficits underlie Autistic Disorders but researchers have got much closer to understanding them in the last five years. This has mainly occurred because the latest research has compared autistic children to other children with the same IQ and chronological age. Deficits appear to be very selective and are not the same in all children with Autism.