The economic cost of supporting someone with autism over a lifetime is much higher than previously thought, research suggests.
It amounts to £1.5m in the UK and $2.4m in the US for individuals with the highest needs, say UK and US experts.
Autism cost the UK more than heart disease, stroke and cancer combined, said an autism charity.
But only £6.60 per person is spent on autism research compared with £295 on cancer, according to Autistica.
The research looked at the costs to society of autism spectrum disorders (ASD) in both the UK and US.
Autism cost the UK at least £32bn a year in terms of treatment, lost earnings, and care and support for children and adults with ASD, found the study, published in the Journal of the American Medical Association Pediatrics.
This compared with £12bn for cancer, £8bn for heart disease and £5bn for stroke, said Autistica.
The figures showed a clear need for more effective interventions to treat autism, ideally in early life, to make the best use of scarce resources, said lead researcher Prof Martin Knapp, of the London School of Economics and Political Science, in London.
"We need to use our resources earlier, identify people earlier and try to provide therapies and support that makes it easier to manage the condition," he told BBC News.
He said new government policies were also needed to address "the enormous impact on families".
Christine Swabey, chief executive of the autism research charity, Autistica, said there was an "unacceptable imbalance" between the high cost of autism and the amount spent on research.
"The right research would provide early interventions, better mental health, and more independence," she said.
"But right now we spend just £180 on research for every £1m we spend on care."
Commenting on the study, Prof Emily Simonoff, of King's College London's Institute of Psychiatry, said the finding was important because of the "relatively low amounts of research funding that go to mental health, despite its huge burden".
More than 600,000 people in the UK have autism, a developmental disorder that can cause problems with social interaction, language skills and physical behaviour.
The disorder varies from mild to so severe that a person may be unable to communicate and need round-the-clock care.
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