A new survey is confirming that large shops and service stations are the worst offenders for selling cigarettes to children.
It is sparking demands for a national crackdown on the problem.
The North Eastern health board carried out the survey in Cavan-Monaghan where seven shop keepers have been prosecuted and fined for selling cigarettes to minors over the past nine months.
Younger shop assistants between 14 and 20 are the most likely offenders.
However the survey has shown a reduction in the problem with 14% of premises visited selling cigarettes to minors compared to 25% last April.
The area's environmental health officers say a national campaign is needed to ram home the message to parents and retailers that it is illegal to get under 18's to buy cigarettes or to sell cigarettes to them.