The goal of this study was to report the long-term effect of different dental health programmes on young adult individuals' knowledge and behaviour relative to oral health. Over a 3 years period, the effect of three different dental health programmes on caries, gingivitis/periodontitis, and knowledge and behaviour concerning oral health in 400 Swedish young adults was evaluated. During the following 2 years, additional prophylactic measures--now based on the individual's symptoms and the prophylaxis previously received--were conducted and evaluated. Five years later still one follow-up was made. The evaluations were based on clinical and radiographic examinations and on a questionnaire survey whose purpose was to study the short- and long-term effects of the different preventive measures, including cost aspects. At the end of the 3 years period, the three test groups exhibited better knowledge and significantly improved behaviour compared with the control group concerning approximal cleaning, from approximately 50% of the individuals at the baseline examination to approximately 90% at the end of the period. Improvement was observed as early as the first year. There were no differences between the test groups. The intensified, individual-related prophylaxis carried out in the following 2 years did not significantly increase knowledge in the test groups; a significant increase in approximal cleaning, however, was found in the control group during this time. At the 10-year follow-up, the individuals' knowledge was undiminished while behaviour concerning approximal cleaning had sunk from 90% to approximately 70% of the individuals. A slight behavioural change concerning number of snacks was found in the course of the study with a shift towards fewer snacks per day. In conclusion, it can be said that simple prophylactic models have an effect on and maintain young adult individuals' knowledge and behaviour concerning oral health and that new knowledge is remembered for long periods of time while changes in behaviour are maintained less well. Moreover, it was found that the scope of the prophylactic programme measured in time and cost had little effect on the long-term result.