Cigarette smoking is the leading preventable cause of death worldwide. Few studies, however, have examined the modified effects of age on the association between smoking and all-cause mortality.In the current study, the authors estimated the association between smoking and age-specific mortality in adults from Beijing, China. This is a large community-based prospective cohort study comprising of 6209 Beijing adults (aged ≥40 years) studied for approximately 8 years (1991-1999). Hazard ratios (HRs) and attributable fractions associated with smoking were estimated by Cox proportional hazard models, adjusting for age, sex, alcohol intake, body mass index, systolic blood pressure, hypertension, and heart rate.The results showed, compared with nonsmokers, the multivariable-adjusted HRs for all-cause mortality were 2.7(95% confidence interval (CI):1.56-4.69) in young adult smokers (40-50 years) and 1.31 (95% CI: 1.13-1.52) in old smokers (>50 years); and the interaction term between smoking and age was significant (P = 0.026). Attributable fractions for all-cause mortality in young and old adults were 63% (95% CI: 41%-85%) and 24% (95% CI: 12%-36%), respectively. The authors estimated multivariate adjusted absolute risk (mortality) by Poisson regression and calculated risk differences and 95% CI by bootstrap estimation. Mortality differences (/10,000 person-years) were 15.99 (95% CI: 15.34-16.64) in the young and 74.61(68.57-80.65) in the old. Compared with current smokers, the HRs of all-cause deaths for former smokers in younger and older adults were 0.57 (95% CI: 0.23-1.42) and 0.96 (95% CI: 0.73-1.26), respectively.The results indicate smoking significantly increases the risks of all-cause mortality in both young and old Beijing adults from the relative and absolute risk perspectives. Smoking cessation could also reduce the excess risk of mortality caused by continuing smoking in younger adults compared with older individuals.