The technique, invented by a team at Boston Children's Hospital, uses EEG scalp scanning equipment used for decades to diagnose epilepsy to spot weaknesses in the brain's wiring.
The researchers who carried out trials on more than 1,000 children aged between two and 12 years found that it was up to 90 per cent accurate in detecting the disease.
The test, they believe, is also suitable for use in poor countries that lack the specialist staff normally needed to make a definitive diagnosis, the Daily Mail reported.
Diagnosis of autism can be a lengthy and complicated process involving psychological tests and the average child is not diagnosed until the age of five and a half.
But Dr Frank Duffy, who led the research, believed there must be a simpler way, and decided to see whether some of the common symptoms of the condition can be traced back to changes in brain activity.
He chose the simpler and cheaper EEG, in which electrodes attached to the scalp tune into brain activity. This revealed striking differences in brain wiring between autistic children and youngsters without the condition.
Connections between brain regions were in general poorer in children with autism.
The differences were particularly apparent in the regions that control language.
"It seemed nearly impossible to even hope that such a consistent pattern could be obtained by a technique that has been around since the 1930s," Dr Duffy said.
The researchers, who detailed their work in the journal BMC Medicine, now want to see if EEGs can be used to pick up Asperger syndrome, which although related to autism, leaves children with different needs. It is diagnosed, on average, at the age of 11.
Other possibilities include predicting same cases of autism ahead of the first symptoms, they said. (More)