Abstract: Objective To examine the association between smoking,body mass index(BMI)and the risk of clinical benign prostatic hyperplasia(BPH),using a hospital-based for surgically treated BPH,case-control study.Methods Cases were men who had surgically treated BPH between 2004 and 2006(n=343),50～82 years old;noncases(controls)were men who had the same age as cases(n=361)who admitted to the same hospital as cases for many different diseases not related prostatic conditions.The cases and controls were inerviewed during their hospital stay,using a self-designed questionnaire that included information on sociodemographic characteristics,anthropometric measures,lifestyle habits(including tobacco smoking and dietary consumption),personal medical history,and family history of prostatism in first-degree relatives.Odds ratios(ORs) and corresponding 95% confidence intervals of variables were estimated using unconditional multiple Logistic regression models.Results After controlling for age and BMI,moderate cigarette smoking was no related with surgically treated BPH(1～29 cigarette/day versus never smoking:OR=0.97,95%confidence interval(CI 0.68～1.46;P trend>0.05),although current cigarette smoking was positively related to BPH surgery only among those who smoked 30 or more cigarettes/day (compared with never smokers:OR=1.32,95%CI0.92～2.58;P trend<0.01).Age-adjusted relative risks for surgically treated BPH in smokers versus nonsmokers stratified by BMI(obesity)were estimated.For men who were both overweight (BMI 24.0～27.9)and obesity(BMI≥28.0),smoking was associated with a significantly increased risk for surgically treated BPH(compared with never smokers:OR=1.68,95%CI1.32～3.67 and OR=2.35,95%CI1.83～4.16 respectively).Conclusion Current cigarette smoking was positively related to BPH surgery only among those who smoked 30 or more cigarettes/day.For men who were both overweight(BMI24.0～27.9)and boesity(BMI≥28.0),smoking was associated with a significantly increased risk for surgically treated BPH.