A US team at Boston Children's Hospital say EEG traces, which record electrical brain activity using scalp electrodes, could offer a diagnostic test for this complex condition.
EEG clearly distinguished children with autism from other peers in a trial involving nearly 1,000 children.
Experts say more work is needed to confirm the BMC Medicine study results.
There are more than 500,000 people with autism in the UK.
Autism is a spectrum disorder, which means that it is not a single condition and will affect individuals in different ways.
Commonly, people with autism have trouble with social interaction and can appear locked in their own worlds.
It can be a difficult condition to diagnose and can go undetected for years.
These patterns consistently spotted autism in children across a range of age groups, spanning from two to 12 years old.
Hallmark brain activity
The researchers repeated their analysis 10 times, splitting up their study group (children with a medical diagnosis of autism and children with no signs of autism) in different ways.
Around 90% of the time, the EEG patterns could correctly detect the children diagnosed with autism.
The team now plan to repeat their study in children with Asperger's syndrome - one particular subset of autism. Typically, people with Asperger's have higher-than-average intelligence and struggle less than people with other types of autism with their speech.
Dr Frank Duffy who is leading the investigation said the work could help determine if Asperger's should be thought of as an entirely separate condition.
And it could point the way to determining if younger siblings of children with autism are likely to develop the same condition themselves.
"It is a great cause of anxiety when an older sibling develops autism.
"EEG might offer a way to check for the same condition in younger siblings in advance of them having symptoms."