A comparison of the principal dental health indices of 13- to 14-year-old Quebec school children between 1977 and 1989-1990 is reported. Data derive from a dental health survey of 1,093 Quebec school children in 1977 and from a province-wide probability sample of 1,342 children in 1989-1990. The most interesting conclusions are: the DMFT index for 13- to 14-year-old children dropped from 9.0 to 4.5; an improvement in the caries treatment level from 26 per cent to 90 per cent is noted; caries treatment needs decreased from 55 per cent to nine per cent; the mean number of extracted teeth per child dropped from a score of 1.6 to a score of 0.03; significant differences in the DMFT index between residential status no longer exist; and no improvement in the oral hygiene condition (OHIS index) is observed. In 1989-1990, 35 per cent of these adolescents had perfect periodontal health. For the others, the principal problems were bleeding gums and/or calculus.