This study assessed the effectiveness and performance of a non-operative caries treatment programme (NOCTP) used since 1987 in the municipality of Nexo in Denmark. The NOCTP emphasizes mechanical plaque control and considers the eruption period of molar teeth as a risk factor. The mean DMF-S among 18-year-olds in 1999 and 2000 in Nexo was 1.23 +/- 2.26 and 1.25 +/- 2.01 (medians 0); 55 and 56% had DMF-S = 0. The mean numbers of sealed surfaces were 4.6 +/- 3.25 and 4.0 +/- 3.22, respectively. The cost per child per year was marginally and significantly reduced in the years with the NOCTP compared to that before 1988 (p = 0.05). In 4 comparison municipalities with very low caries experience, mean DMF-S scores among 18-year-olds in 1999 were 2.73-3.25 (medians 1-2) and were significantly higher than in Nexo (p < 0.001). The NOCTP differed from the preventive programmes used in the comparison municipalities in the period 1988-1999 in emphasising care for the erupting molars, the use of a firm guideline and stated goals to be achieved, but with less emphasis on diet. The effectiveness and performance of the NOCTP were both considered high, as very low DMF-S and high %DMF-S = 0 had been achieved by 1999, and 18-year-olds in Nexo had significantly less caries than in the comparison municipalities. The latter difference could not be explained by difference in caries-related background variables.