Failure to correctly diagnose the special needs of children could lead them to self harm, it has been claimed.
One expert warned parents also fear their children are suffering mental health problems because autism spectrum disorder is not being recognised.
The Welsh Government has invested £13m in an autism service but it does not offer help to those yet to be assessed.
It said parents who have concerns about their children should contact their GPs.
Nicky Heady said an earlier Asperger’s Syndrome diagnosis for her daughter Caitlin might have saved her much anguish.