The number of new cars licensed for the first time in January was 26% lower than in the same month last year.
CSO figures show a 26% drop in private cars and a 19% drop in the number of goods vehicles licensed during the month.
The drop in the January numbers comes on the back of a disappointing year for the motor industry in Ireland. Car sales were down 12% in 2012.
Motor tax was increased in December's budget.
Car retailers are hoping a new license plate regime, with two separate number plates to indicate whether a car was licensed in the first half or second half of the year, will spread sales more evenly across 2013.
Traditionally the opening months of the year are when the vast majority of new cars are sold.