According to figures from car history service Motorcheck.ie, the figures for the month of March are down 7.5pc.
The top selling manufacturers were Toyota, Ford, Volkswagen, Hyundai and Nissan. The top selling models were the Hyundai Tucson, Nissan Qashqai, Ford Focus, Skoda Octavia and Volkswagen Golf.
Light Commercial Vehicles are down 10.66pc year to date over 2016.
Motorcheck's Michael Rochford says the industry is coming off three years of solid growth and it was generally considered that 2017 would see a levelling off.
"Annual growth of 30pc year-on-year was never going to be sustainable," he says in the service's monthly commentary on the state of the motor trade. He added that factors relating to the dip include uncertainty over Brexit, as well as the strength of the euro over sterling has also made it attractive to import used cars from the UK.
Used car imports for quarter one were 56pc higher than the first quarter of 2016.
