Over 2,600 Irish residents travelled to the North for private healthcare in the space of 18 months.
According to Freedom of Information figures, this cost the HSE over €9 million.
The Northern Ireland Planned Healthcare Scheme was introduced at the start of last year.
It allows Irish residents to get private healthcare in the North and be reimbursed by the HSE.
The most common treatments people get are orthopaedics and eyecare.
Just under 1,200 people availed of the scheme last year, costing the HSE just over €4 million.
That increased to over 1,400 patients in the first six months of this year, costing almost €5 million.
Independent TD Michael Healy-Rae organises buses to leave Kerry to allow people have cataract surgery in the North under the scheme.
"I do the logistical organisation between the hospital and the patient.
"I book the buses, I use a Kerry transport company, and I use the same hotel - so I get the best rates to try and minimise the cost.
"90% to 95% of the money is reimbursed"
He said people travel to the North to avoid long waiting lists here.
"Quite simply because if you wait to be done in the Republic, the odds are you will go blind".
In the same 18-month period, over 2,400 travelled to the European Union under a similar scheme, called the Cross Border Directive.
This cost the HSE nearly €9.9 million.