Estimating the proportion of lung cancer deaths that can be avoided is important in assessing the potential impact of anti-smoking efforts on the reduction of lung cancer deaths. We calculated the population attributable risk (PAR) and absolute risk of lung cancer death according to smoking status based on the Japan Collaborative Cohort (JACC) Study. The analytic cohort included 45,010 males and 55,724 females aged 40-79 years. Cox proportional hazards model was used to determine age-adjusted relative risks and PAR according to smoking status. We also computed lung cancer mortality according to age and smoking status. In males, 52.2% and 14.8% of lung cancer deaths were attributable to current and former cigarette smoking, respectively. In females, the corresponding figures were 11.8% and 2.8%. Among current male smokers, the relative risk was strongly correlated with the intensity and duration of cigarette smoking. In contrast, the PAR was associated with an intermediate level of smoking except for the years of smoking: the largest PARs were observed in those with 20-29 cigarettes per day, 40-59 pack-years and 20-22 years old at starting smoking. Absolute risks were estimated to increase with age and duration of smoking and not to decrease even after cessation. These findings suggest that avoidable lung cancer deaths are primarily among light to moderate smokers who are considered amenable to population-based antismoking strategies. For all current smokers, immediate cessation is encouraged because it offers the only realistic way to avoid a substantial increase in lung cancer mortality brought about by further continuation of smoking. (C) 2003 Wiley-Liss, Inc.