Measurements and Main Results: A total of 1,100 lung cancer deaths were observed during the 26-year follow-up period. Each 10 μg/m3 increase in PM2.5 concentrations was associated with a 15–27% increase in lung cancer mortality. The association between PM2.5 and lung cancer mortality was similar in men and women and across categories of attained age and educational attainment, but was stronger in those with a normal body mass index and a history of chronic lung disease at enrollment (P < 0.05).