Between June and November 1983, the "Quit. For Life" media campaign was conducted in Sydney to reduce the prevalence of smoking. Surveys on a cross-sectional sample of the Sydney population were conducted before and after the campaign, and similar measures were undertaken in the rest of Australia for comparison. The sample sizes for both the Sydney and control areas comprised more than 4000 subjects. In addition, a cohort of 949 residents of Sydney and Melbourne were followed for changes in the prevalence of smoking during the year of the campaign. The cross-sectional survey results for 1984 and 1983 demonstrated decreases in the prevalence of smoking of approximately 1% for both men and women in Sydney compared with the rest of Australia. In the cohort study there was a 3.4% decrease in smoking prevalence in Sydney compared with a 0.8% increase in Melbourne. The pooled estimate of the difference in smoking prevalence attributable to the campaign was 2.8% (95% confidence interval, 0.5%-5.1%).