| CDC research About 300,000 U.S. children have been diagnosed with autism, according to the largest national study so far of the prevalence of this complex behavioral disorder.
That means about 5.5 out of every 1,000 school-age children have been diagnosed with autism.
Past estimates have ranged from 1 to 9 out of every 1,000 children, based on smaller studies in individual states or cities.
The government-run study released Thursday reports findings from national surveys of tens of thousands of families.
The study by the U.S. Centers for Disease Control and Prevention also found boys are nearly four times more likely than girls to be identified with the condition. And it found Hispanics had lower autism rates, though it's possible that may be related to health-care access problems.
The study does not attempt to answer whether autism is increasing -- a topic, driven in part by a debate over whether autism is linked to a vaccine preservative. The new research is being published this week in the CDC publication, Morbidity and Mortality Weekly Report.