Children with autism are facing delays in access to specialist care because they are not being diagnosed early enough, experts have said.
Researchers from Newcastle University said the age of diagnosis has not decreased in a decade - still averaging four-and-a-half years.
Researchers analysed data concerning 2,100 children between 2004 and 2014 for the study which was published in the Journal of Autism and Developmental Disorders.
Jon Spiers, chief executive of Autistica, the autism research charity that funded the study said ways to speed up diagnosis were needed, especially for "those left isolated for too long, such as girls with autism".
A separate report published by the National Autistic Society, includes a survey of more than 7,000 people with autism, their family members, friends and professionals.
The findings, released ahead of World Autism Awareness Day on Saturday, show:
79% of autistic people and 70% of family members feel socially isolated
84% of autistic people said people judge them as strange
50% of autistic people and family members said they are so worried about how people will react to their autism that they "sometimes or often" don't go out
74% of family members said people tut or make disapproving noises about behaviour associated with their child's autism
The National Autistic Society is calling on the public to find out more about autism so they can respond to autistic people with more understanding.