Ceftriaxone (1 g, intravenous administration, 30 to 60 minutes preoperatively) was the only antimicrobial therapy used for 103 male patients undergoing transurethral surgery. Only patients who had sterile urine were included in the study. Patients with a preoperative catheter placed were excluded. One transurethral incision of the prostate, four direct-vision internal urethrotomies, and 98 transurethral resections of the prostate were performed. Urine specimens for culture were obtained preoperatively and on first voiding after catheter removal for all patients. During the first postoperative visit (11 to 40 days after surgery), urinalysis was performed for all patients, and specimens for culture were obtained from 89 patients. No infections were noted on cultures of first voided specimens after catheter removal; there were four infections (3.88%) on first postoperative visit cultures. No significant morbidity occurred secondary to urinary tract infection. According to these findings, the use of antimicrobial agents beyond the preoperative and immediate postoperative period in uninfected patients undergoing transurethral surgery does not appear to be indicated.