A basic problem in dental health education (DHE) is that the effect usually disappears shortly after the termination of a program. The purpose of the present study was to obtain long-term effect of a DHE-program by emphasizing the active involvement of the participants. The sample comprised an experimental and a control group, each of 68 unskilled workers, aged 18-64. Active participation was obtained by various means: Teaching was carried out in pre-existing peer groups, the participants' own goals and needs were included, the traditional dentist-patient barriers were excluded, the traditional dentist-patient roles were changed, and the sessions were repeated. No dental treatment was included. The control group did not participate in the DHE-programme. Plaque (PII) and gingivitis (GI) were scored before the program, immediately after, and 6 months and 31/2 yr after the last session. In the experimental group PII and GI decreased significantly from 1.30 and 1.42 at baseline to 0.39 and 0.97 6 months after the program, and 0.45 and 0.79 31/2 yr after the termination of the program. It is suggested that the reason for the long-term effect obtained in the present study was the use of the principle of active involvement of the participants in the DHE-program.