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Although smoking and alcohol has been linked to an increased risk of colorectal neoplasm (CRN), large-scale studies to identify dose-dependent relationship between amount of smoking and alcohol consumption and risk of CRN are rare. We aimed to investigate the risk for CRN according to the amount of smoking and alcohol intake in a large sample of Korean adults.A cross-sectional study was performed on 31,714 examinees aged ≥30 years undergoing their first colonoscopy as part of routine preventive health care between 2010 and 2011. Never smokers were compared with six groups of smokers according to smoking amount, and individuals with alcohol intake of ≤ 6.25 g ethanol per day were compared with three groups according to alcohol amount.In adjusted models, the risk of overall CRN increased with increasing amount of smoking (P for trend 0.001). The adjusted odds ratios for overall CRN comparing never smokers with six smoker groups according to smoking amount (≤2.50, 2.51-5.60, 5.61-9.00, 9.01-13.00, 13.01-19.50, and ≥19.51 pack-years) were 1.02, 1.19, 1.35, 1.53, 1.63, and 2.03, respectively. In addition, the risk of both non-advanced and advanced CRN increased with increasing amount of smoking (both P for trend 0.001). However, the amount of alcohol consumption was not correlated with the risk of CRN.The prevalence of CRN was associated with increasing amount of smoking in a dose-response manner, whereas it was not associated with the amount of alcohol consumption. Our study suggests that smoking amount as well as smoking status should be considered for CRN risk stratification.