The aim of the study was I) to compare the caries prevalence of preschoolchildren in Baja with data from 1975 and 2) to evaluate the effect of 0.2% sodium-fluoride mouthrinsings practiced during the last 4 yr. In 20 kindergartens of Baja 1462 children between 3 and 6 yr of age were investigated. All the children were participants in an oral hygiene motivation program and fluoride rinsings, performed generally monthly, but at least 10 times in a year. The dental investigations of the primary teeth were carried out by the same team as in 1975. The frequency of caries-free children increased from 18.8% in 1975 to 24.8% in 1982. The dmft mean values decreased only in the 5- and 6-yr-old children.