U.S. health officials on Thursday called the disorder an urgent public health concern.
The new numbers based on the largest, most convincing U.S. study done so far trump previous estimates that placed the prevalence at 1 in 166.
The difference means roughly 50,000 more children and young adults may have autism and related disorders than was previously thought.
Government scientists declined to call the results a complete surprise: The new estimate is on the high end of a prevalence range identified in other recent studies, they said.
But one advocate said the study should cause policy-makers and the public to revise how they think of autism.
"This is a greater national health care crisis than we thought even yesterday," said Alison Singer, spokeswoman for Autism Speaks, the nation's largest organization advocating services for autistic children.
The study should fuel efforts to get the government to spend hundreds of millions of additional dollars for autism research and services.
"This data today show we're going to need more early intervention services and more therapists, and we're going to need federal and state legislators to stand up for these families," Singer said.
The study by the U.S. Centers for Disease Control and Prevention was based on 2002 data from 14 states. It calculated an average autism rate 6.6 per 1,000, compared to an estimate last year of 5.5 in 1,000.
The new research involved an intense review of medical and school records for children, and gives the clearest picture yet of how common autism is in some parts of the country, CDC officials said.
The results suggest 560,000 children and young adults have the condition.
However, the study population is not demographically representative of the nation as a whole, so officials cautioned against using the results as a national average. The study does not include some of the most populous states, such as California, Texas and Florida, reports AP.
Also, the study does not answer whether autism has recently been on the rise a controversial topic, driven in part by the contention of some parents and advocates that it is linked to a vaccine preservative. Scientific studies have not borne out that claim.