Your child's doctor will look for signs of developmental delays at regular checkups. If your child shows some signs of autism, you may be referred to a specialist in treating children with autism. This specialist, working with a team of professionals, can perform a formal evaluation for the disorder.
Because autism varies widely in severity and manifestations, making a diagnosis may be difficult. There isn't a specific medical test to pinpoint the disorder. Instead, a formal evaluation consists of an expert observing your child and talking to you about how your child's social skills, language skills and behavior have developed and changed over time. To help reach a diagnosis, your child may undergo a number of developmental tests covering speech, language and psychological issues.
Although the signs of autism often appear by 18 months, the diagnosis sometimes isn't made until age 2 or 3, when there may be more obvious delays in language development and social interactions.