This study was undertaken to determine the impact on ejaculatory function of tamsulosin (0.2 mg) given once daily (OD) for 12 weeks and to identify risk factors for ejaculatory dysfunction in patients undergoing this treatment.Males with an International Prostatic Symptom Score (IPSS) ≥8 were enrolled in this study.All participants completed questionnaires,including the IPSS and the Male Sexual Health Questionnaire (MSHQ),and serum prostate-specific antigen,transrectal ultrasound and uroflowmetry with post-void residual were measured.After initiating 0.2 mg OD tamsulosin,patients were re-evaluated on the fourth and twelfth weeks of medication.The chi-squared test,the independent t-test and one-way ANOVA were used to compare means.Binary logistic regression analysis was used to calculate the odds ratio for all risk factors.A total of 177 men constituted the study cohort.No significant difference was observed between baseline and follow-up for the erectile function,ejaculatory function,satisfaction,sexual activity and desire domains (EFD,EjFD,SDA and ADD) or for erectile or ejaculatory bother mean scores.After 12 weeks,the overall incidence of ejaculatory dysfunction (EjD) was 13.4％.Incidences of the seven different types of EjD (decreased frequency,delay,dryness,decreased strength/force,decreased volume,decreased pleasure and pain at ejaculation) were 2.4％,3.1％,3.9％,3.9％,6.3％,7.1％ and 3.1％,respectively.Baseline EjFD scores were higher for I PSS responders than for non-responders (26.09 vs.24.06,P=0.03).An EjFD score reduction was more frequent in IPSS responders.The incidence of EjD was small,but not negligible and was more frequent in patients with less lower urinary tract symptoms,a smaller prostate,higher baseline MSHQ totals and higher EjFD scores.