The NHS is failing youngsters with autism, a charity warned today.
More than 70% of children with autism also have a mental health problem which is preventable or treatable, such as depression or obsessive compulsive disorder.
According to the National Autistic Society (NAS), these issues are often dismissed by health workers as "unfortunate" or "unavoidable" side-effects of autism.
One mother told the NAS her two teenagers with autism were self-harming and had tried to commit suicide but the family was only offered group therapy with a nine-month waiting list.
The NAS said another self-harming woman who was in hospital following a suicide attempt was told she had attachment disorder rather than autism. Her mother was blamed for not nurturing her as a baby. A diagnosis of autism was eventually reinstated.
Mark Lever, chief executive of the NAS, said children are often failed because their mental health issues can be difficult to diagnose.
Launching the charity's Need to Know campaign, he said: "Too many children with autism are developing preventable mental health problems and find themselves up against a broken system that doesn't understand them or their needs.
"All too often they receive inappropriate, ineffectual and sometimes harmful treatments.
"This has a devastating effect on families, many of whom develop their own mental health problems as a result.
"Parents and professionals alike are crying out for more autism support.
"The NHS needs to know how to help them, and the Government needs to know it can't wait."
A survey of 455 parents for the campaign found that 208 had children currently registered with mental health services.
Of these, 43% (90) said their child's mental health had got worse because they could not access the services they needed.
Meanwhile, more than half of parents said they did not think mental health staff knew how to communicate with their child.
And, in 90% of cases, mental health problems had made a negative impact on the mental health of the whole family.
More than a quarter of family members needed support from mental health services as a result, the poll found.
Some 83% of the children first experienced mental health problems before the age of 10 and half before the age of five.
The NAS said too many health professionals have no basic autism training while many need support to adapt treatments for autistic children.