A comparison was made between the dental health of children in two Scottish towns, one of which was fluoridated until 1983. The mean decayed, missing and filled (dmft) score was found to be 69 per cent lower in 5-year-old children in the fluoridated town compared with the non-fluoridated one and there was a similar 65 per cent difference for DMFT scores in those aged 15 years. 10-year-old children in the fluoridated town had a 39 per cent lower DMFT score, less than the 50 per cent difference found in the 1980 study. Comparison with an identical 1980 study allowed secular trends in caries prevalence to be examined. This revealed a 13 per cent reduction in dmft scores for 5-year-old children and a 16 per cent reduction in DMFT in 10-year-old children in the non-fluoride town. There was a 52 per cent reduction in dmft in 5-year-old children in the previously fluoridated town; however those aged 10 years had a higher DMFT score in 1986 than in 1980. Although this study found that there is a residual benefit from fluoridation in all age groups, there are indications of an adverse trend in dental health in the 10-year-old children in the fluoridated town. The investigation confirmed that the trend is towards lower caries levels amongst Scottish schoolchildren.