Children identified as being potentially autistic have to wait an average of almost six months for an initial assessment in Yorkshire.
National guidelines recommend children are seen within three months of referral.
Of 2,026 Yorkshire children currently in need of assessment, 913 have exceeded the target timeline.
A spokesperson for The National Autistic Society (NAS) said long delays could be “devastating” for families.
Research by the BBC found NHS Airedale, Wharfedale and Craven Clinical Commissioning Group (CCG) had the longest average wait at 47 weeks.
Of the 190 children in current need of assessment, 148 have already waited for more than three months.
Vale of York CCG had the second longest average wait at 34 weeks.
Bassetlaw CCG and Sheffield CCG reported the shortest average waits at four and six weeks respectively.
Autism is a developmental disorder that can cause problems with social interaction, language skills and physical behaviour.
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