But health officials say the new number may not mean autism is occurring more often. Much of the increase is believed to be from a cultural and medical shift, with doctors diagnosing autism more frequently, especially in children with milder problems.
There are no medical tests for autism, so diagnosis is not an exact science. It's identified by a child's behavior.
This latest estimate by the Centers for Disease Control and Prevention means autism affects roughly 1.2 million U.S. children and teens.
Thursday's report is considered the most comprehensive on the frequency of autism.
To learn more about autism spectrum disorder, visit www.cdc.gov/autism
To learn more about CDC's "Learn the Signs. Act Early" program, visit www.cdc.gov/ActEarly
To learn more about CDC's Study to Explore Early Development, visit www.cdc.gov/SEED