Q: What is the prevalence of autism?

A: Although the exact prevalence of autism is not yet known, estimates range from one-in-500, to one-in-1,000 cases in the United States. Current statistics show that autism occurs in all racial, ethnic, and social groups, and that boys are three-to-four times more likely to be affected.

Initial studies done in the 1960s indicated that autism had a prevalence rate of four-to-five cases in 10,000, which is why the condition was thought to be rare. However, current prevalence estimates are not consistent with prevalence rates for a rare disease. Further, recent U.S. and international data point to a steep increase in prevalence of the condition.

However, many epidemiologists believe that recent changes in diagnostic criteria and in the conditions that are classified as autism spectrum disorders could account for some of the increased prevalence.

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