Met Éireann have issued a Status Yellow fog warning from tonight for four counties.
The warning will come into place at 9pm tonight and remain in place until 10am on Friday morning.
Counties affected are Cork, Limerick, Tipperary and Waterford.
Motorists and other road users are asked to take extra care when travelling while the warning is in place.
The Road Safety Authority (RSA) is reminding motorists to always use fog lights when driving in dense fog and remember to turn them off once the fog has cleared.
Fog can affect judgement of speed and makes tail lights appear further away than they really are.
The RSA said it is essential drivers slow down and drive at a safe distance from the vehicle in front.