The periodontal condition of the inhabitants of Jönköping County, Sweden was followed for 20 years by means of 3 cross-sectional investigations performed in 1973, 1983, and 1993. The study comprised individuals in the age groups 20, 30, 40, 50, 60, and 70 years. The number of dentate individuals was 537 in 1973, 550 in 1983, and 552 in 1993. All individuals participating in the studies were examined clinically and radiographically. They also filled out a questionnaire about dental care habits, socio-economic status, and general health. A clear reduction in the plaque score was seen between 1973 and 1983 in all age groups. With one exception, no further significant change in plaque levels was found between 1983 and 1993: the increase in plaque among the 20-year-olds was significant. In 1993 the mean % of surfaces with plaque was between 30% and 40% in all age groups. Gingivitis values corresponded well with the values of dental plaque; the same pattern with a clear reduction in gingivitis score was seen in all age groups between 1973 and 1983, and an increase in the mean frequency of gingival inflammation between 1983 and 1993 was seen in the 20-year age group. 30% of the individuals in this age group had more than 50% gingivitis in 1993 compared with 9% of the individuals in 1983. The 20-year-olds were further analyzed in a linear regression model using gingivitis as a dependent variable against some socio-economic, general health, and dental care variables associated with poor oral hygiene and gingivitis. In 1993, the most important explanatory variable was gender: significantly more males than females had higher gingivitis scores. The second most important explanatory variable was toothbrushing habits. Together they explained 10.9% of the variance. The multivariate analysis did not reveal approximal cleaning habits to be significant, probably due to their strong connection to gender and toothbrushing habits. In the 1983 sample, no significant explanatory variables were found. It was concluded from this data that it is important not only to renew but also to direct preventive guidelines more towards young adults who have no previous extensive experience of oral disease so that they will not be excluded from dental care and their dental health thereby jeopardised. In addition to preventive programmes aimed at the population as a whole, individual programmes based on risk targeting are also necessary to reduce the number of people developing dental disease and to increase the quality of dental care.