The diagnostic criteria for autism spectrum disorders has largely been based on the behavioural characteristics of boys and men.
Charities are now campaigning for changes, to recognise the more nuanced way girls and women may present with the condition.
That is what has just happened in Scotland.
The Scottish Intercollegiate Guidelines Network, which produces clinical practice guidelines for the NHS in Scotland, published new guidance in July.
Consultant psychiatrist Iain McClure, who helped draw up the guidelines, says there is growing evidence showing differences in how males and females with autism present.
"A teenage girl with autism might for example be integrated into a peer group, and often they're talking about how they're pretending to be normal," he says.
"They're trying to fit in with the group and they are following the same sort of interest that the peer group have got but perhaps in a more bizarre or unusual way.
"So, when you actually get into the detail, you start to see how this problem is more camouflaged but still subtly present."
Iain McClure is convinced there are many women and girls who are developing mental health problems, anxiety, depression, eating disorders, because their actual condition is not being spotted.
"I keep seeing patients who have got autism, but we didn't know they had it," he says.
"What's happened is they've developed a kind of burnout.
"So, it's really important to try and recognise these difficulties as early as possible.
"Knowledge is power - if you understand a problem you can do something about it."