Not so long ago it was thought that only boys had autism. But there is growing evidence that autism among girls is a hidden problem that we just don't see or understand,
Because the condition looks different in young women and girls, some families wait many years for a diagnosis and even longer to get proper help.
Our social affairs correspondent Christine Alsford has the first of three special reports to mark Autism Awareness Week.
Firstly, she meets two families from near Aylesbury who are sharing their stories to raise awareness of the condition that's all too often misunderstood.
Interviewees: Lily (12); Mandy Chivers, mother; Dr Will Mandy, Clinical Psychologist, University College London; Sarah Lyst, mother; Niamh (12).
The National Autistic Society run a confidential helpline on 0808 800 4104. You can contact the campaign group Fighting Inequality for Girls on the Spectrum at firstname.lastname@example.org