The president of the High Court has said the director general of the Heath Services Executive must inform him as a matter of urgency how it plans to deal with the impact of Brexit on wards of court who are placed in specialist units the UK.
Mr Justice Peter Kelly said he had been previously told the matter was "under consideration" by the HSE but it would have to be "more proactive".
He is concerned about "what is going to happen" as a result of Brexit, he said.
He directed the general solicitor for wards of court to write on Tuesday to the director general of the HSE asking what plans it has to deal with the situation.
If there is no response within 14 days, he will list the matter, the judge added.
He made the comments when dealing with the situation of an adolescent girl who is receiving treatment in a specialist unit in the UK for an eating disorder.
Several other young people from here are receiving similar treatment while other children and adults are receiving specialist treatment there not available here for a range of conditions.
The judge said he would be reviewing the adolescent girl's case just a month before Brexit and wanted to know the HSE's plans in relation to wards of court who are either in the UK now or who are likely to be subject of applications to be placed there between now and the Brexit date of March 2019.
It is important there is "some clarity" concerning the legal regime, he said.
If there was no response from the HSE within 14 days, he would list the matter because the court needed to know and could not have a "legal vacuum".
Those wards of court who are in the UK now were placed there under European Framework legislation and avail of services provided by the NHS in the UK, he said.
That system had to date worked very well but he did not know if it would still be available post Brexit or if it would function in the same way.
He suspected things would not be as simple as they are now where wards can be speedily moved to the UK when their circumstances are urgent, he added.