All children should have routine developmental exams by their pediatrician. Further testing may be needed if there is concern on the part of the clinician or the parents. This is particularly true whenever a child fails to meet any of the following language milestones:

• Babbling by 12 months
• Gesturing (pointing, waving bye-bye) by 12 months
• Single words by 16 months
• Two-word spontaneous phrases by 24 months (not just echoing)
• Loss of any language or social skills at any age.

These children might receive a hearing evaluation, a blood lead test, and a screening test for autism. A health care provider experienced in the diagnosis and treatment of autism is usually necessary for the actual diagnosis. Because there is no biological test for autism, the diagnosis will often be based on very specific criteria laid out in a book called the Diagnostic and Statistical Manual IV.

The other pervasive developmental disorders include:

• Asperger syndrome (like autism, but with normal language development)
• Rett syndrome (very different from autism, and only occurs in females)
• Childhood disintegrative disorder (rare condition where a child acquires skills, then loses them by age 10)
• Pervasive developmental disorder - not otherwise specified (PDD-NOS), also called atypical autism.

An evaluation of autism will often include a complete physical and neurologic examination. It may also include a specific diagnostic screening tool, such as:

• Autism Diagnostic Interview  - Revised (ADI-R)
• Autism Diagnostic Observation Schedule (ADOS)
• Childhood Autism rating Scale (CARS)
• Gilliam Autism Rating Scale
• Pervasive Developmental Disorders Screening Test-Stage 3

Children with known or suspected autism will often have genetic testing (looking for chromosome abnormalities) and perhaps metabolic testing.

Autism encompasses a broad spectrum of symptoms. Therefore, a single, brief evaluation cannot predict a child's true abilities. Ideally, a team of different specialists will evaluate the child. They might evaluate speech, language, communication, thinking abilities, motor skills, success at school, and other factors.

Sometimes people are reluctant to have a child diagnosed because of concerns about labeling the child. However, failure to make a diagnosis can lead to failure to get the treatment and services the child needs.