Landlords have registered more than 100,000 properties with the State body responsible for regulating the sector, new figures show.
A number of factors appear to be behind the rise, including greater awareness of the registration process and growing levels of second-home ownership.
However, with an estimated 150,000 private rented properties in the State, thousands of landlords are continuing to flout the law by failing to register with the Private Residential Tenancies Board.
Landlords are legally obliged to register their property if they are renting it out on a full-time basis as a residential property. Short-term holiday home lettings are not included. Landlords who fail to register face fines of up to €3,000. Just 20,000 landlords had registered with the board after a deadline to do so expired in December 2004, but registrations recently topped 100,000.
The old landlord registration system operated by local authorities had just 25,000 properties listed.
While tenancies board chairman Tom Dunne said substantial progress had been made, he still urged tenants to contact the office if they believed their landlord was not registered.
"We are regularly asked to check tenancies for registration by a wide variety of groups, including residents associations. Where they are not registered, landlords are pursued to ensure they register the tenancies concerned."