Background: A consortium of six research groups estimated the impact on lung cancer mortality of changes in smoking behavior that began around the publication of the Surgeon General's report (SGR). This chapter presents the results of that effort. We quantified the cumulative impact of changes in smoking behaviors on lung cancer mortality in the United States over the period 1975–2000. Methods: The six groups used common inputs and independent models to estimate the number of U.S. lung cancer deaths averted over the period 1975–2000 as a result of changes in smoking behavior beginning in the mid fifties, and the number of deaths that could have been averted if tobacco control had completely eliminated all smoking following issuance of the first SGR on Smoking and Health in 1964. Results: Approximately 795,000 deaths (550,000 men and 245,000 women) were averted over the period 1975–2000 as a result of changes in smoking behavior since in 1950s. In the year 2000 alone approximately 70,000 lung cancer deaths were averted (44,000 among men and 26,000 among women). However, these represent approximately 30% of lung cancer deaths that could have potentially been averted over the period 1975–2000 if smoking was eliminated completely. In the 10-year period 1991–2000, this fraction increased to about 37%. Conclusions: Our results show the substantial impact of changes in smoking behavior since the 1950s. Despite a major impact of changing smoking behaviors, tobacco control effort are still needed to further reduce the burden of this disease.