Autism is a complex developmental disability that typically appears during the first three years of life and is the result of a neurological disorder that affects the normal functioning of the brain, impacting development in the areas of social interaction and communication skills.  Both children and adults with autism typically show difficulties in verbal and non-verbal communication, social interactions, and leisure or play activities.  One should keep in mind, however, that autism is a spectrum disorder and it affects each individual differently, and at varying degrees, and this is why early diagnosis is so crucial.  By learning the signs, a child can begin benefiting from one of the many specialized intervention programs. 

Autism is one of five disorders that falls under the umbrella of Pervasive Developmental Disorders (PDD), a category of neurological disorders characterized by "severe and pervasive impairment in several areas of development".

The five disorders under PDD are:

• Autistic Disorder
• Asperger's Disorder
• Childhood Disintegrative Disorder (CDD)
• Rett's Disorder
• PDD-Not Otherwise Specified (PDD-NOS)

Each of these disorders has specific diagnostic criteria which have been outlined in the American Psychiatric Association's Diagnostic & Statistical Manual of Mental Disorders (DSM-IV-TR).