Thousands of autistic students leaving school are being lost by the system and missing out on opportunities for further education, MPs have warned.
Connexions, the advice service for teenagers and under-25s with learning difficulties, did not know what happened to nearly a third of autistic students, the Commons public accounts committee said.
With autism prevalent in about 55 in 10,000 of the population, it suggests more than 6,000 of the 20,000 under-25s with this type of learning difficulty have been lost in the system.
Edward Leigh, the committee's chairman, said: "Adults with autism are being left to fend for themselves, with all the consequences this has for their access to further education, benefits or employment, and for their mental health.
"A critical point is the transition from the relatively structured framework of services for children to adulthood. It is like being cast adrift."
Local authorities are supposed to provide colleges with Section 140 statements detailing students' continuing needs for educational support after schooling, but college disability-support officers said they were often vague or of poor quality.
One told the National Audit Office: "Section 140 assessments in general are useful. However, they are fraught with problems, as they are not standard throughout Connexions as an organisation.
"Connexions should make more effort to provide historical information, especially statements of educational need, educational psychologists' reports, medical history on the condition, etc, as this would help the learners when moving into further education."
The committee also recommended autism training for Connexions advisers.