First described by Leo Kanner in 1943, autism is the most common of these disorders, with a prevalence rate of 2-5 per 10,000. The ratio of autism spectrum disorders to boys is 3:4. Autism syndrome, along with a number of other developmental disorders listed in both the ICD-10 and DSM-IV, is open to further analysis and study.

Like autism, Asperger syndrome is characterized by abnormalities in interaction and restricted, repetitive patterns of activities and interests. However, it differs from autism in that it does not have delays in language development or intellectual development. According to the authors, people with Asperger syndrome have an excellent memory for facts and figures.

Like autism, Rett syndrome is characterized by abnormalities in social and language development and is accompanied by repetitive patterns of behavior. It is important to note that these problems are not evident at birth. Symptoms of the disorder occur between 5 and 30 months of age and are accompanied by mental retardation. Severe and profound cognitive impairments accompany Rett syndrome, and epilepsy usually occurs before adolescence. The syndrome has been observed only in girls.

Childhood disintegrative disorder (or Heller syndrome) includes social, communicative, and behavioral features of autism, but follows at least two normal developmental periods.