New car registrations for October, at 1,946, were 13.8% lower than for the same month a year ago, new figures from the Society of the Irish Motor Industry show.
For the first ten months of the year, new registrations are down 10.3% at 130,504.
However, the number of used imported vehicles being registered here in October was 20.1% higher than October 2016 at 8,509.
For the year to date, almost 80,000 used cars have been brought into the country, a rise of 35.6% on the same timeframe last year.
Car sales have contributed €1.39 billion to the Exchequer so far this year.
Other notable data compiled by SIMI/Done Deal show petrol (+5.7%) and diesel (+5.3%) prices are considerably higher than they were a year ago, while the average price of a new car is down 3.5% and insurance costs are 14.3% lower.
But average insurance costs in September were 44.8% higher than in September 2013.