OBJECTIVES Worldwide, the association of smoking with development of lung cancer has been ascertained. However, it remains unknown of the magnitude of the association in the Chinese population. We thus systematically reviewed the published studies worldwide. METHODS We searched Medline, EMBASE, and three other Chinese databases from their inception to June 2008. We included case-control and cohort studies that investigated the association of smoking with lung cancer, and that provided data on the magnitude of the association. Two reviewers screened the eligibility, assessed the extent of bias, and extracted data independently. We obtained unadjusted and adjusted estimates of studies. We pooled the trial data using random-effect model and explored the heterogeneity by the pre-specified variables. RESULTS We included 45 (n=71,869), 4 of which were cohort studies (n=48,250) and 41 case-control studies (cumulative cases: 10,268, and controls: 13,351). Smoking increased the risk of lung cancer by 137% (OR 2.37, 95%CI 1.95 to 2.88). Pooling of adjusted estimates of in 32 studies showed that the risk of lung cancer was increased by 181% (2.81, 2.31 to 3.42). No gender difference was found in the association (15 studies): ORs were 3.19 (2.51 to 4.06) in male and 2.98 (2.29 to 3.89) in female (interaction p>0.1). The risks were statistically different in different type of lung cancer: adencarcinoma 1.81 (1.23 to 2.66), squamous cell carcinoma 7.07 (2.34 to 21.38), and small cell lung cancer 7.98 (4.22 to 15.11). The increased amount of smoking increased the risk of lung cancer (coef. 0.27, 0.03 to 0.51). No significant dose-response was found between the risk of lung cancer and the duration and initiating age of smoking. CONCLUSIONS The association between smoking and lung cancer has been ascertained in the Chinese population. Pronounced heterogeneity in risks of lung cancer was found in different type of lung cancer and amount of smoking.