This paper describes the evaluation of a massmedia periodontal health campaign lasting for 3 months in 1981. The public-directed campaign succeeded a dentist-directed training period of 1 year and comprised television and radio programmes, articles in newspapers and weekly magazines and a pamphlet presenting five common-sense rules for the care of teeth. To assess the effect of the campaign on exposure, awareness, knowledge, attitude, intention and behaviour were measured by interviewing representative samples of the Norwegian population aged 15 years or more in 1981, 1982, 1983 and 1985. The percentage of the interviewees who had received information about dental health through mass media increased. From the baseline survey in 1981 to 1983 a significant increase was found in the percentage who had correct knowledge of periodontal health. No specific effect of the campaign was, however, found concerning people's daily use of dental floss and toothpicks. Multiple classification analyses revealed that knowledge and gender were the strongest predictors of dental health behaviour across all years of the investigation. In conclusion, the impact of campaigns like this will be greater if: (i) involvement of the audience is encouraged, (ii) the message is simple and repeated over a longer period of time via multiple channels and (iii) more emphasis is given to the pre-programme planning, including defining the goals and target group explicitly, pretesting the message and selecting channels relevant for the target group.