New figures from the Society of the Irish Motor Industry show that new car sales in January were down 4.8% on the same time last year.
The latest SIMI figures show that 37,125 new cars were sold in January, down from 39,003 in January of 2017.
But used car imports in January rose by 20.3% to 9,061 from 7,532 the same time last year on the back of continued weakness in sterling.
The SIMI figures also showed that new electric car sales fell by over 38% in January of this year - slowing to 104 compared to 168 in January 2017.
They also reveal that the top selling car in January of this year was the Hyundai Tucson.
SIMI also said that for all of last year, new car registrations fell by 10.4% to 131,355.
Car sales contributed a total of €1.49 billion to the Exchequer last year, down 1.5% on the previous year.
Meanwhile, the average cost of a new car was down 2% last year, but petrol prices rose by 4.2% while diesel prices increased by 3.6%.
Alan Nolan, SIMI's director general, said that 2017 finished down 10.4% as anticipated and also recorded a shift in the market-share of diesel cars from 70% to 65%.
"The same trends have been apparent in January's new car sales, which have delivered a steady start to the 181 registration period," Mr Nolan said.
But he noted that Brexit has continued to impact with new car sales down 4.8% while used car import registrations are up 20% compared to January last year.
He said that while the number of electric cars registered in January shows a decline on last year, this was a timing issue with supply and later new model delivery dates.
The sector remains confident that EV registrations will increase significantly in 2018, he added.