Damaging misconceptions about autism in Wales mean 17% think children with the condition are "simply badly behaved," new research has found.
Autism can lead to communication difficulties among those diagnosed
The National Autistic Society Cymru (NAS Cymru) said 43% thought most people with autism had special ability in maths and art, for example.
NAS Cymru attributed this to the "continuing endurance of the Rain Man stereotype," following the 1988 film.
It is starting an awareness campaign on autism, which impairs communication.
It is estimated that autism, including Asperger's syndrome, affects more than 26,000 people in Wales.
Autistic people can have difficulties forming social relationships, have problems with verbal and non-verbal communication and develop strong narrow obsessional interests.
NAS Cymru's Think Differently - Act Positively report said the research revealed confusion about who is affected by autism and whether it is a lifelong condition.
Some 44% of people surveyed were aware that there is no cure and 27% of those who had heard of autism mistakenly believed it mostly affected children.
In the film Rain Man, Dustin Hoffman played a character with autism who also had a remarkable maths talent. In fact, according to the report, such abilities are extremely rare.
The research also found that the public would be far more willing to engage with people with autism if they understood more about the condition. Three-quarters said they would be happy to work with someone with autism.
Dustin Hoffman played an autistic savant in the film Rain Man
But while the research identified some goodwill, the report said it does not always translate into action.
There were continuing problems with finding help for autistic children in education, with parents often having to battle for the right support, the report said.
Shirley Parsley, NAS Cymru's national co-ordinator, said living with autism could often be an isolating experience.
"By encouraging people to think differently and understand more about autism, NAS Cymru hopes to improve the lives of thousands of people with the condition," she said.
"We are calling on the public, professionals and government to act positively to ensure people with autism have the same rights and freedoms as the rest of society."
As part of the campaign, NAS Cymru is calling on the Welsh Assembly Government to lobby the UK Government to ratify the UN Convention on the Rights of Persons with Disabilities.
The society also wants the assembly government to take action to increase awareness of autism, tackle discrimination and improve training.