Scientists in Britain have created a brain scan that could screen children for autism within 15 minutes.
Tests on adults show the scan, which measures changes in the brain, has a 90% accuracy.
It could completely change psychiatrists' methods of diagnosing the disorder.
The scan is quicker - and up to 20 times cheaper - than current ways of spotting autism, which affects more than 500,000 people in the UK.
The brain scans take a matter of minutes and cost between £100 and £200.
Although it is likely to be used as an extra diagnostic tool at first, in time the technique could replace observational assessments completely, the researchers believe.
Autism spectrum disorder (ASD) is the name given to a range of conditions caused by abnormalities in brain development.
Dr Christine Ecker, a leading member of the Institute of Psychiatry team, said: "The value of this rapid and accurate tool to diagnose ASD is immense. It could help to alleviate the need for the emotional, time consuming and expensive diagnosis process which ASD patients and families currently have to endure.
"We now look forward to testing if our methods can also help children."