Abstract Since 1968, six caries clinical trials have been conducted in the North-West of England by different examiners using the same diagnostic system, and a steady reduction in caries prevalence in 11–12-yr-old schoolchildren has been recorded. In the present study, five of the examiners revisited some of the schools which participated in their original trials and each examined between 196 and 296 children. The time intervals between the original and repeat examinations were 12, 10, 8, 5 and 3 yr. Percent caries reductions (PCRs) ranged from 19 to 33 for DMFT and from 24 to 35 for DMFS but the PCRs did not relate to the time intervals between examinations. The PCRs were greater on free smooth and approximal surfaces than on fissure surfaces and for the anterior teeth than for the mouth as a whole, suggesting that fluoride may have played a role in the reductions.