Australian officials currently estimate that about one in 160 children are diagnosed with autism, but findings from two new studies suggest it is much more common.
It is not clear whether autism itself is on the rise, or whether better diagnosis is inflating the figures.
Researchers from Melbourne's La Trobe University studied 20,000 children as they grew from infants to toddlers.
They trained baby health nurses to pick up early signs of autism.
Dr Cheryl Dissanayake is one of the lead researchers.
"So what we're finding from the SACS study is that one in 119 children are meeting criteria for an autism spectrum disorder at the age of two years," she said.
"These data are in accordance with the data coming out of the UK."
'One in 100'
Professor Margot Prior says a second independent study from the university found the figure was close to one in 100.
"Well we had 19 autistic children in a sample of 1,900. So that's one in a 100. So again, we believe that the prevalence is certainly greater for whatever reason," she said.
"And of course this is a population, you know, a non-clinical sample, just from the population out there. "
It is still unclear whether there are more cases of autism or whether doctors are just more aware of the condition and likely to pick it up.