This report describes a clinical study carried out to compare the cariesinhibiting effect of the unsupervised home use of a sodium-monofluorophosphate-calcium-carbonate-based toothpaste formulation and an acidulated phospho-fluoride (APF) gel professionally applied semi-annually, used singly and together. The study was of 3 years’ duration, involving 1,718 boys and girls aged 11–12 years at the time of the initial examinations, living in two sectors, London and the Isle of Wight. There were five treatment groups: control group – non-fluoride paste and non-fluoride gel; paste A group -fluoride paste A and non-fluoride gel; paste B group – fluoride paste B and non-fluoride gel; gel group – non-fluoride paste and APF gel, and paste A/gel group – fluoride paste A and APF gel. Paste A and paste B differed in their flavour systems. The study was of double-blind design and included annual clinical and radiographic examinations. After 3 years, there were statistically significant reductions in caries increments when the test and control groups were compared. However, the unsupervised use of sodium monofluorophosphate dentifrice was as effective in reducing caries as twice annual, professionally applied, treatments of APF gel. Further, the reductions in caries obtained by the combined use of fluoride dentifrice and gel applications were not significantly greater than the use of fluoride dentifrice or gel applications alone. Detailed analysis of the data revealed disparities in the effect of treatment related to sex and sector.