BACKGROUND: Lung cancer incidence is gradually leveling off in developed countries but is continuing to rise in Korea. Because of the rapid increasing in smoking prevalence among women and youngers, the lung cancer incidence is expected to increase within next three and four decades. The aims of the present study are to analyses the smoking habits in patients with lung cancer and to evaluate of the relative risk of smoking habits in patients with lung cancer. METHOD: The present investigation was hospital-based, case control study. It included data from 93 case subjects with lung cancer and 1132 controls with disease unrelated to smoking using smoking history questionnaire by direct personal interview. RESULT: Compared with non-smoker, those who smoked more than 50 years had an odds ratio for lung cancer of 8.8(1.8-20.7). The odds ratios was 8.5(3.5-20.7) for those whose total number of cigarettes per days exceeded 41 and 5.5(2.3-13.3) for men with started habitual smoking less than 20 years old. The risk was increased in men with more than 41 pack years of cigarette smoking(OR:5.5, 95% CI:2.6-11.9). Odds ratios associated with cigarette smoking were 2.5(1.1-5.8), 5.1(2.6-10.4) for exsmoker and current smoker, respectively and 2.2(1.0-4.6) for non-filter smoker with more than 16 years. CONCLUSION: There was a clear dose-response relationship between the risk of lung cancer and smoking. We conclude that smoking dose is important risk factor for lung cancer and smoking habits may be, also.