The number of new cars licensed in the year to July fell by 11.3%.
The Central Statistics Office (CSO) says there were 6,164 cars licensed last month compared with 6,953 in July last year.
Over 3/4 of the cars licensed were diesel.
The number of new goods vehicles increased though by 13.5%.
There were 6,164 new private cars licensed in July 2012, compared with 6,953 in July 2011, a decrease of 11.3%.
The licensing figures also show that in July the total number of all vehicles licensed was 12,113 compared with 13,496 in the corresponding month last year.
While of the 6,164 new private cars licensed 22% were petrol and 76.2% were diesel.
The highest number of new private cars licensed in July 2012 – classified by make was Volkswagen (883) followed by Ford (735), Toyota (637) and Renault (486).