It is one of the varieties of pervasive developmental disorder. It is a disorder characterized by severe and pervasive impairment in several areas of development such as social interaction skills, communication skills, or the presence of stereotyped behaviour, interests and activities.

There are various criteria used in diagnosing autism.

Difficulty with social relationships.

Difficulty with verbal and non-verbal communication.

Difficulty in the development of play and imagination.

Resistance to change in routine.

All these symptoms must have been present by 36 months of age

In autism, there are one or several abnormalities in the brain, which are caused by one or several biological factors such as Genetic factors, Maternal rubella, Lack of oxygen at birth, Excess of oxygen at birth, Encephalitis, Untreated phenylketonuria, Tuberose sclerosis. This is known as "the biological theory of autism"

Serotonin has been found to be contributory in either genesis or maintainance of Autism. However, detailed studies have to be carried out to confirm this possibility.

Following are the autistic behavioural pattern

Social behaviour - unresponsiveness to people, lack of attention to people, reacting parts of people as detached objects, lack of eye contact, treating people as if they were inanimate objects, lack of behaviour appropriate to cultural norms, attention to the non social aspects of people, lack of awareness of the feelings of others, lack of social perceptiveness, Failure to develop a concept of mind - MIND BLINDEDNESS.

Language - Abnormalities in speech i.e. they cannot produce sounds that are recognizable as words is called as FUNCTIONALLY MUTE CHILDREN. In those children with autism who do develop speech, a variety of unusual features are sometime (but not always) seen. These include Echolalia (words/phrases, which are echoed either immediately after they are heard or sometime later and persist even after the age of 3yrs),

Neologism (coining new words to give meaning to things) or saying 'you' when they mean 'I' or calling themselves by their first name.

Repetitive, obsessive behaviour - Lack of flexible imagination coupled with obsessive behaviour e.g. counting lampposts, collecting bottle tops etc. their play is very uncreative.

Islets of ability - Children with autism often perform unusually well in drawing, music and calendar calculations. Sometimes they are the only skills a child has and sometimes they are even superior to normal