Allied Irish Banks has claimed 4% of its mortgage customers have decided not to repay the money.
In an address to a cross-party group of politicians, AIB chief executive David Duffy also claimed that 2,000 customers in arrears have cash deposits big enough to clear their debts.
And on the investment side of its business, Mr Duffy said the bank has found 1,000 accounts where buy-to-let investors had intended to use rental income to pay for their lending but are now using the money for other needs.
Mr Duffy is the first of the country's top bankers up before the Oireachtas Committee on Finance to discuss the financial services sector and activities within the four main lenders.
Committee chair Ciaran Lynch said the meetings aim to help find sustainable, long-term solutions to the mortgage crisis and measures to ease the burden on struggling homeowners and distressed borrowers.
Last month, the Central Bank revealed that 98,000 mortgage holders were in arrears by 90 days or more at the end of June.
AIB also issued a series of figures on how it has handled the mortgage arrears crisis on its books.
:: "Permanent resolutions" agreed in 4,400 accounts with 2,579 securing capitalisation; 1677 having term extension; 182 voluntary sale; and 17 put into a split mortgage.
:: 12,500 offers have been made to customers in relation to resolving arrears.
:: A total of 153 split mortgages have been agreed.
:: More than 5,000 legal letters have been issued to customers to kick start engagement with the bank on arrears.
:: One quarter of all buy-to-let mortgage holders have not made any repayments in the last six months.