Girls are at risk because it takes too long recognise when they have autism, parents say.
Autism in girls, which is more subtle than in boys, often goes undetected and disadvantages their health and school life, the parents said.
Autistic Advocacy Network New Zealand founder Gabrielle Hogg, who is also autistic, said behavioural studies of autism had mostly been about males.
While boys tended to physically isolate themselves and avoid eye contact or social situations, girls on the spectrum hid their traits to fit in.
"Girls learn how to mimic other people," she said.
"They may take on other personalities of people in the classroom, they may take on a mother figure, or somebody they have watched on TV."
Anxiety, trauma and depression were high in autistic women, and early intervention would save lives, Ms Hogg said.
It usually took a mental health crisis such as self-harming before diagnosis was made, she said, and autistic women or girls were often misdiagnosed with borderline personality disorder or bi-polar disorder.
"There is all this stigma out there when you present differently as a girl."
Teachers, mental health professionals and pediatricians needed more training so they could pick up the signs, Ms Hogg said.
Autism NZ's Dane Dougan said there was no data on autism in New Zealand, which made it difficult to research.
While overseas figures show about 1 in 66 people are on the autism spectrum - which would amount to about 60,000 people in New Zealand - only around 8000 receive disability support for autism, he said.
Sometimes having a diagnosis of autism was not enough to access support, particularly if there was not an intellectual disability too, he said.
"It's really challenging," he said.
"Just because they don't have an intellectual disability, they still need help sometimes. To be turned away from these crisis situations is just not right."
The Ministry of Health should prioritise autism and collect thorough data for research purposes, he said.
'She may not have survived'
Timaru woman Sandi said her daughter Sarah*, now 16, was about 7 or 8 years old when she began self-harming and was 12 when she first tried to commit suicide.
It was "heartbreaking" and "soul-destroying", Sandi said.
"There was no support for me, I didn't know how I should treat her, so I walked around on eggshells."
After that, Sarah was in and out of child mental health services for years, with one child psychologist labelling her naughty and attention-seeking.
Dissatisfied with this explanation, Sandi began her own research.
"All my research led me to aspergers, everything I read."
Sandi said Sarah had found it hard to make friends at school and copied all of her sister's interests. She would come home from school frustrated and anixous, and even now could not walk to the bus alone or handle strangers or pressure.
Aided by her Child and Adolescent Mental Health worker, Sarah was tested 18 months ago and officially diagnosed as high-functioning aspergers.
"I wouldn't change my girl for the world," Sandi said.
"She just needs the right person to give her that extra support, somebody who actually knows what they're doing, because I'm just flying by the seat of my pants."
Sandi said the health system failed her daughter for not picking up the traits first and, without diagnosis, she may not have survived.
* Name has been changed