Some people visited a Belfast A&E unit 17 times last year, the BBC has learned.
Figures show that 131 patients attended the emergency department at the Royal Victoria Hospital in Belfast 2,240 times during 2013.
The figures were obtained under the Freedom of Information Act.
In Altnagelvin Hospital in Londonderry, 58 people were responsible for 876 attendances at the A&E there.
The figures showed that 98 people made 1,588 visits to the emergency department at Craigavon Area Hospital.
In Antrim Area Hospital, 67 people made a total of 1,340 visits last year.
Statistics also revealed that one person made 35 trips to the casualty department in the Tyrone County Hospital last year; one made 14 visits to the same hospital in 2012 and in the previous year one person made 40 trips there.
Sean McGovern of the South Eastern Trust said most people had a genuine reason for attending.
"We have to be very clear this is a wide spectrum of people who, at the upper end, will attend once a week or perhaps more.
"They tend to be homeless patients, patients with alcohol or drug addiction and then there are people who will attend once a month who have chronic illness or have a real need."
He said there were "targeted measures to treat these patients".
Health Minister Edwin Poots said: "Right across the UK there are a small number of people using emergency departments an unprecedented amount of times.
"Medical staff rightly point out that people using emergency departments for non-urgent ailments are putting a strain on resources.
"I would urge people to think carefully about how they use the health service should they or their family become unwell or have an accident.
"Emergency Departments provide the highest level of emergency care for patients, especially those with sudden and acute illness or severe trauma.
"I don't want to discourage those with a genuine medical emergency from calling 999 or attending an emergency department, but simply ask that they choose well and consider the range of other more appropriate services available."
The data also indicated that across the UK, some patients were attending more than 50 times a year.
Data from 183 sites revealed nearly 12,000 people throughout the UK made more than 10 visits to one unit in 2012-13.
A small number of those - just over 150 - attended more than 50 times.
Doctors warned that the issue, while confined to a minority of patients, was adding to the mounting pressures on the system this winter.
As part of the investigation, the BBC asked 175 hospital trusts and boards across the UK for information on repeat attendances during 2012-13. A total of 106 responded, covering 183 units.