The prevalence of dental caries in 10-year-old children in Stranraer has increased since the withdrawal of water fluoridation, with a 115% increase in the mean cost of restorative dental work due to caries and a 21% increase in the mean cost of all dental treatment. In Annan, a similar town which has never had fluoride added to the water supply, caries prevalence fell significantly, with little change in the cost of dental treatment. The findings suggest an association between cessation of water fluoridation and the increased prevalence of caries in Stranraer children.