More than €458m (£413m) was spent in Northern Ireland by shoppers from the Republic of Ireland in a 12 month period.
The figures have been released by the Republic of Ireland's Central Statistics Office.
The bulk of the spend, nearly €287m (£259m), came from people living along the border.
For some this is about convenience, whereby a northern town is their nearest shopping destination.
For those living in County Louth villages like Omeath and Carlingford, a trip to Newry is a shorter distance than travelling around or over the Cooley Peninsula to Dundalk.
Colm Shannon, chief executive of Newry Chamber of Commerce and Trade is keen to stress this convenience.
"Christmas has been really buzzing in Newry," he said.
"Obviously cross-border trade is really important to us and Dublin is only really an hour away, so a significant proportion of the population of Ireland is only a short distance too."
Analysis: Brexit impact?
By Mark Simpson, BBC Newsline Reporter, in Newry
It is the final Christmas before Brexit and border retailers in Northern Ireland are making the most of it.
TVs, medicines, washing powder and alcohol are proving particularly popular.
Few believe that much will change immediately after the UK leaves the EU - which is due to happen at the end of March - but the worry is that attitudes may be different.
There has been so much hype - and misinformation - around Brexit that southern shoppers may be less willing to travel north even if the border is unchanged.
But for many other visiting shoppers it is price and not convenience that is the deciding factor.
The figures were calculated by the Central Statistics Office in the 12 months up to the first quarter of 2018.
The "Newry-effect" was a term coined a decade ago. It represented the flood of visiting shoppers to border towns and cities based on price differentials and exchange rates.
At the time, the Republic of Ireland's economy appeared to be in freefall and the euro had reached near parity with the pound, meaning huge savings were there for the taking.
A new motorway meant Dublin shoppers could be in Newry in an hour, with many of the safety concerns and trading restrictions of the past a distant memory.
From a young age monitoring the euro-sterling exchange rate becomes part of the daily routine on both sides of the border.
Most shops in Newry take euro and two of the banks in the city have euro-only ATMs.
This is a reality for border people that defines everything from where you get your groceries, where to go on a Saturday night, where to fill your petrol tank and even where to get married.
Speaking to southern shoppers in the car park of the Quays Shopping Centre, all were able to quote the exchange rate to within 1p of its rate that day.
About one third of the shoppers in the centre's expansive car park had southern registration plates.
Whilst not an exact science, it would appear that the vast majority were from Louth, then Monaghan, Meath and Dublin.
Most said they were there for price differentials on alcohol and groceries.
A mother and daughter from Dundalk said they had made the short journey for a different range of shops than were available 13 miles down the road.
One thing few of the visiting shoppers intended to do was fill their fuel tanks - pointing out that this commodity remained cheaper in the Republic of Ireland.
And according to Declan McChesney who runs a local family owned shoe shop, business on the border is all about ebb and flow.
"Newry has forever dealt with the rises and falls of sterling and the euro and we build our businesses to level it out between us to make sure we remain competitive and make it worthwhile for our southern customers to come up," he said.
"Sometimes we have to absorb the swing and other times it helps us a little. In terms of southern trade it's been a steady year and customers have continued to come up."
It's this year-round view, rather than a desire to cash in for Christmas that has sustained the Newry appeal through the Republic's economic recovery and regularly fluctuating exchange rates.
Choice, price, convenience and consistency of offering have benefitted Newry, not just this Christmas but for the past decade - even if the offering is sometimes slightly different.
Tucking in to a bag of southern Tayto before heading home, one visiting shopper joked that he liked the northern equivalent just fine.
Other brands of crisps are of course available on both sides of the border.