ObjectiveTo examine the effects of hypertension on lung cancer prospectively and to determine the interactive effect of hypertension and smoking on lung cancer risk.DesignA prospective cohort study.ParticipantsThe cohort comprised 452 645 Korean men, aged 35–64 years, who received health insurance from the Korea Medical Insurance Corporation and who had biennial medical evaluations in 1992 and 1994.MethodsMultivariate Cox proportional hazard models were tested, controlling for age, smoking status, exercise, body mass index, alcohol use, diabetes and serum cholesterol concentration.Main outcome measureDeaths from lung cancer.ResultsAt baseline, 261 080 persons (58.3%) were identified as current cigarette smokers. Between 1995 and 1999, 883 deaths from lung cancer (44.8/100 000 person-years) occurred. An initial finding indicated that hypertension increased the mortality risk of lung cancer [risk ratio (RR) 1.3, 95% confidence interval (CI) 1.1–1.5]. However, after stratification for smoking status, the risk ratio was increased only for current smokers (RR 1.4, 95% CI 1.2–1.6). When the interaction term was included in the multivariate model, there was a significant interactive effect of hypertension with current smoking (RR 1.8, 95% CI 1.0–3.1) on the risk of death from lung cancer, whereas the effect of hypertension itself did not attain significance.ConclusionHypertension was not an independent risk factor in lung cancer-related deaths, but it increased the modest risk of lung cancer death among current smokers.