PURPOSE: Transrectal ultrasound-guided prostate needle biopsy (TRUS-PBx) is the standard procedure to diagnose prostate cancer. We evaluated the incidence and risk factors of infectious complications, the species cultured and rates of resistance for antibiotics of microorganism in infectious complications after TRUS-PBx. MATERIALS AND METHODS: We retrospectively evaluated the medical records of 742 patients who underwent TRUS-PBx from January 2004 to May 2007. All patients were treated with intravenous ciprofloxacin and oral ciprofloxacin for 1 week after discharge. Patients who presented infectious complications were performed chest x-ray, blood analysis, urine analysis and culture studies. RESULTS: Among 742 patients, 15 patients (2.0%) developed infectious complications. There were no significant differences between the complication and non-complications groups in age, PSA, prostate volume, nodule, hypoechoic lesion on transrectal sonography and underlying medical diseases. Twelve cases were performed in outpatient department and 3 cases were in operation room and that suggests high frequency of infectious complication when transrectal prostate biopsy is performed in outpatient department (p=0.007). Six kinds of microorganisms were cultivated in 12 patients (1.9%). E. coli (7/12) was most common. Extended-spectrum beta-lactamase suggesting nosocomial infection was positive in 3 cases of outpatient department. On logistic regression analysis, urethral catheter indwelling was a significant risk factor increasing infectious complications. CONCLUSIONS: After TRUS-PBx, the rate of severe infectious complications and nosocomial infections were more frequent in outpatient department. And urethral catheter indwelling significantly increased infectious complication rate. So we should sublate the urethral catheter and keep in mind the aseptic technique at outpatient department.