Government departments and local health and social care organisations do not have enough information on the number of adults with autism, a report from the National Audit Office has warned.
The spending watchdog said there is also a lack of understanding and awareness of the condition.
This has limited the ability of government departments to plan and deliver services effectively, the study said.
Around 400,000 adults in England have autism and the report suggested that many of these people require specialised support.
But the NAO discovered that most NHS organisations do not have records of how many people they treat for autism.
Increasing the identification rate of those with autism by just eight per cent could lead to potential savings of £67m a year, the NAO estimated.
The report also stated that organisations often fail to secure appropriate support for the 200,000 or so adults with autism who do not have a learning disability.
Health and social care services have processes to work with people with a learning disability, a physical illness or mental health problems - but autism is not covered.
And those with autism also lack specialised employment support, the NAO warned. It said that the lack of understanding was a "significant barrier" to employment for adults with the condition.
Auditor general Tim Burr said: "Greater awareness of the numbers of people with autism, as well as better understanding of autism amongst those providing health, social care, benefits, education and employment services, would lead to improved quality of life for those on the autistic spectrum.
"Specialist support and joint working across all areas - clinical, social and employment - could improve the transition from childhood to adult services, make services more effective and improve value for money."
Chairman of the public accounts committee Edward Leigh said that many adults with autism were "slipping through the net".
"They do not fit into any particular category for which services are provided: many do not have a learning disability, a physical disability or a mental health problem and therefore fail to qualify for any help whatsoever," he said.
"For young people with autism, the difference between the services available to them as children and those available to them as adults is stark. The move into adulthood must be like falling into an abyss."
The report recommended a more targeted approach to support for people with high-functioning autism and Asperger Syndrome.
