A follow-up study of the dental health of children resident in two towns in south-west Scotland, one of which had fluoridated water until 1983, was carried out at the end of 1988. Comparison with an identical 1980 study allowed trends in the prevalence of caries to be examined. In 1988, the mean, decayed, missing and filled deciduous teeth (dmft) score for 5-year-old children in Stranraer, the formerly fluoridated town, was 3.08, 24 per cent worse than the score of 2.48 reported in 1980. In Annan, mean dmft for 5-year-old children was 3.18 in 1988, 27 per cent lower than the 1980 dmft score of 4.38. The difference in caries prevalence between the two towns in 1988 was a non-significant 3.1 per cent compared with the 44 per cent difference found in 1980. Similar trends in caries prevalence were also found in 10-year-old children with mean DMFT scores of 2.28 in Stranraer and 2.56 in Annan in 1988, a 10.9 per cent difference compared with the 50 per cent difference reported in 1980. The Stranraer DMFT score was 37.4 per cent higher than the DMFT of 1.66 recorded in 1980, while in Annan, the mean DMFT of 2.56 was 23.6 per cent lower than the 1980 score of 3.35. The comparison confirms a trend to lower caries levels in Annan children in line with the general trend in caries prevalence in much of western Europe. However, despite the almost universal use of fluoride toothpaste, caries prevalence in Stranraer children has increased since fluoridation ceased to almost parity with children in the non-fluoridated area. This study shows that there is still a benefit to be gained in terms of lower caries rates by implementing water fluoridation despite the general decline in dental caries.