Although autism isn't diagnosed by a medical test, some tests may be ordered to rule out other medical problems that could account for the symptoms. According to the National Institute of , symptoms usually show up by age three, and continue throughout life. Autism is sometimes suspected when babies or toddlers don't behave or develop as would be expected for their age. Children living within this spectrum often appear relatively normal in their development until the age of two or so. Parents may start to notice delays in language, play or social skills. These symptoms alone don't confirm a diagnosis of autism, but are taken into consideration when evaluating children. comprehensive evaluation that can include consultation with a neurologist, specialized pediatrician, psychologist, speech/language therapist or any other professional skilled in the diagnosis or treatment of autism and its effects.

In addition to observing a child, professionals attempting to make a diagnosis may ask for specific input from parents or other caregivers. important to distinguish between autism and other developmental disabilities, behavior disorders, hearing problems or eccentric behavior so that an appropriate treatment program can be started as soon as possible. Unfortunately, these disorders can also be present in the child with autism, making diagnosis that much more difficult.

babies and children who seem to be developing normally sometimes lose abilities they already had, like talking. This is called a regression. since they don't respond to questions and situations the same way other children do.