Car sales fell by 1.7% in January, when compared with the same month last year, according to new figures from the Society of the Irish Motor Industry.
There were 39,019 new cars sold last month, while the corresponding figure for January 2016 was 39,722.
Light commercial vehicle sales fell by 2.4% (6,394) compared with January last year (6,555), while heavy goods vehicle registrations are were 6.3% lower at 456.
Meanwhile, SIMI also said total new car sales for 2016 were 17.5% higher than the previous year and the industry contributed €1.5 billion to the Exchequer.
On the cost of motoring, the industry body said the average price of a new car was 5.5% lower last December, when compared with the same month in 2015.
However, petrol (+1.9%) and diesel (+3.2%) prices have both risen in the last year, and insurance costs are 61.5% higher than they were in 2013.
On the outlook for car sales this year, the author of SIMI's research, Economist Jim Power, said: "Looking ahead to 2017, while the outlook for car sales is a bit more difficult to predict than last year, the projected growth in personal disposable incomes and the availability of credit provide solid support for car sales.
"However, the impact of Brexit and the increased volume in imported used cars are other issues that may impact on new car sales this year.
"Overall, though, numbers should be fairly close to last year with perhaps a slight decline of around 3% in new car sales in 2017, which would imply new car sales of around 142,000."