Federal health officials say greater awareness, broader definitions and spotting autism in younger children may explain some of the increase in the proportion of children with disorders.
Two new government studies indicate about 1 in 100 children have autism disorders, higher than a previous estimate of 1 in 150.
Dr. Thomas Insel, director of the National Institute of Mental Health, says the main concern is determining whether there's a "true increase" in the numbers. The new estimate would mean about 673,000 American children have autism. Previous estimates put the number at about 560,000.
One of the studies stems from the 2007 National Survey of Children's Health. The results are in October's Pediatrics. The other government estimate is from the Centers for Disease Control and Prevention and has not been formally released yet.