Autism is almost five times more common in boys than in girls, and also has a higher diagnosis rate in white children. It is also diagnosed more often in white children.
Autism can be spotted as early as age 2, but the average age in the report was between four and five-years-old.
The rates of diagnosis rose 30 percent between 2008 and 2010, and have more than doubled both nationwide. The CDC estimates that 1.2 million people under the age of 21 are on the autism spectrum.
Epidemiologist, Walter Zahorodny at Rutgers New Jersey Medical School who directed New Jersey data-collection for the report, said this would put to rest the argument over whether autism diagnoses are actually increasing.
"It's a true increase," he said. "It's a change of great magnitude. It's silly to go on debating that."
The CDC's Boyle sidestepped the "why" question by saying there is evidence that some of the increase is due to changes in diagnosis without elaborating on what is responsible for the rest of it.
The disorder is characterized by communication problems, obsessional interests, and repetitive movements. Diagnosis is based on symptoms, not a medical test. Symptoms for people who are on the autism spectrum can range from mild to severe.
The official description of autism was changed last year when a new Diagnostic and Statistical Manual of Mental Disorders, the DSM-5, was published. The new CDC report used the old definition. Some autism advocates are concerned that the new definition will reduce the number of children with the diagnosis, leaving fewer kids eligible for special services.