Some children diagnosed as autistic at a young age see their symptoms completely disappear when they get older, new research shows.

The small-scale study -- published in the "Journal of Child Psychology and Psychiatry" -- included 34 subjects who were diagnosed very early on with the disorder but who, by ages 18 to 21, no longer exhibited any signs of it.

Unlike when they were little, the subjects no longer showed deficits in speech, communication, recognizing faces or social interactions -- all hallmarks of autism.

"Although the diagnosis of autism is not usually lost over time, the findings suggest that there is a very wide range of possible outcomes," said Thomas Insel, director of the National Institute of Mental Health.

Previous studies had already suggested it was possible for an autism diagnosis to disappear over time.

But this research looked deeper into the legitimacy of the phenomenon. The authors questioned whether the initial diagnosis had been accurate and whether the subjects had truly caught up to their peers.

In both cases, it turned out the answer was yes.

The researchers, led by Deborah Fein of the University of Connecticut, reviewed the original reports written when the children were diagnosed and had them examined by additional experts outside the research group.

The data was compared to groups of young adults whose diagnoses of autism and its milder sibling, high-functioning autism, persisted, and to a control group.

The analysis showed that, among the 34 subjects whose autism symptoms had abated, doctors had originally observed lower levels of social deficits than among the subjects with high-functioning autism.

But other symptoms, including language delays and repetitive behavior, had been on par with the other group.

And the contemporary testing of the study subjects -- all of whom attended school in mainstream classrooms with no special services -- confirmed that the young adults no longer exhibited any deficits.

But the authors emphasized that the study offers no insight on what percentage of children with autism spectrum disorder, or ASD, will grow out of their diagnosis.

"All children with ASD are capable of making progress with intensive therapy, but with our current state of knowledge most do not achieve the kind of optimal outcome that we are studying," said lead author Fein.

"Our hope is that further research will help us better understand the mechanisms of change so that each child can have the best possible life."