18,776 new cars were licensed in May, a drop of 3.4% on the same month a year earlier, according to the Central Statistics Office.
For the first five months of this year, the figures show a fall of 7.9% to 91,534.
The number of second-hand vehicles licensed fell by 16.8% compared with May 2001, while new goods vehicles showed a 4.5% decline.
The total number of all vehicles licensed in the first five months of this year was 124,488, compared with 136,422 in the same period last year.
