A 3-year clinical trial was carried out in France just after fluoride toothpaste was allowed to be sold on the mass market. The aim was to assess the caries preventive effect of a toothpaste containing the maximum fluoride level permitted by the EEC (1.2% SMFP). The trial started with 1318 10-12-yr-old children from a wide socioeconomic background in a typical French community. Test toothpaste was given to 659 children whereas the remaining 659 children obtained the same toothpaste without the fluoride additive. The brushing was unsupervised and performed by the children at home. Dental caries was assessed by clinical and radiographic examinations. 1061 children completed the trial. An interview carried out at the final examination identified a group of 116 uncooperative children (less than five brushings a week on average) who were not included in the statistical analysis. The following mean reductions were found: 26% for DMFT, 27% for DMFS, and 39% for DMFSU. The DMFS index for approximal, buccal-lingual and occlusal surfaces showed caries reductions of 32%, 25%, and 22%, respectively. The trial demonstrated a highly significant effectiveness of the 1.2% SMFP toothpaste in a French population.