Spending in Ireland by overseas visitors rose by nearly a fifth last year.
An additional €661m were spent in Ireland compared with 2014, tourism authorities said.
Tourism Minister Paschal Donohoe said: "Today's figures confirm that 2015 was an exceptional year not just in terms of overseas visit numbers but also the associated revenue which totalled over €4.2bn.
"The good news is that we are aiming for even further growth in visit numbers and associated revenue in 2016 and a strong marketing campaign is already under way.
"Of course this being St Patrick's week, Tourism Ireland's Global Greening initiative is taking place across the world at a time when many people are planning their holidays, giving Ireland an unparalleled platform to encourage people to pay us a visit."
Spending in Ireland by overseas visitors for last year rose by 19% compared with 2014.
The data also shows that the number of trips to Ireland in the key target market of holidaymakers rose by 20%, while spending by holidaymakers was up 28% for 2015 when compared with 2014.