More than 3,500 needs assessments for children with disabilities are overdue completion.
83% are at least three months late.
An 'assessment of need' allows a child to be diagnosed with a disability, such as autism, and then apply for the care they need.
The HSE is legally obliged to have these assessments finished within six months.
But according to the HSE's latest figures, that target isn't being met in many cases.
3,503 assessments are overdue.
They include 1,016 in north Dublin, along with 814 in Cork, 127 in Meath and 89 are in Waterford.
Lorraine Dempsey, the interim chief executive of Inclusion Ireland, says the assessments are vital.
She said: "If a parent wanted their child enrolled in an autism-specific class, because they're exhibiting all of those signs and there's a question mark over it without the actual clinical diagnosis on paper by a psychologist, the parent can't even apply for a place in those classes."
"There are certain barriers that children will face if they don't get a specific diagnosis."
Of the national total, 83% of the overdue assessments are at least three months late.