New car sales fell by 31 per cent in August, according to figures from the Central Statistics Office (CSO).
The decline follows the ending of the scrappage scheme in June.
Overall, 3,653 new private cars were licensed last month, compared with 5,310 for the same month a year earlier.
There were 968 new goods vehicles licensed last month, an increase of 4.5 per cent on the 926 registered in August 2010.
The total number of all new vehicles licensed fell by 23.8 per cent to 5,275 last month.
The number of all vehicles licensed in August 2011 fell by 14.3 per cent from 11,753 in August 2010 to 10,007 last month.
Volkswagen was the most popular brand for new car sales, followed by Ford, Renault and Toyota.
Recent figures from the Society of the Irish Motor Industry (SIMI) also show a bid decline in new registrations.
Those figures indicate that new registrations fell 36 per cent to 3,242 in August compared to the same month a year earlier.
However, sales for the first eight months of the year were reported to be up by 7 per cent at 84,412.
