Severe frost and ice rendered roads in many parts of the country extremely dangerous this morning, with Co Donegal particularly badly hit.
Gardaí in Co Donegal advised motorists not to drive due to adverse weather conditions. Nearly 40 vehicles were involved in eight separate crashes across the country.
One man (24) was killed in a collision between a car and a truck shortly after 11pm on the N15 at Friarsbush between Donegal town and Ballybofey.
There were no other deaths or serious injuries reported.
The N15 Donegal to Ballybofey road remains closed, while the through road from Laghy to Castlederg has been closed due to ice. Motorists are being diverted via Glenties, which is also said to be icy.
The N13 between Lifford and Letterkenney and the main Lifford to Derry road were said to be treacherous this morning.
Several collisions were reported on the R265 Lifford to St Johnston road.
Icy conditions and black ice are also widespread in counties Longford, Meath and Leitrim. Drivers are warned to avoid the Mullingar to Lanesborough road.
Police in Derry said three cars ploughed into a ditch after careering off a road in the city. There were no reports of injuries.