We determine if a single 500 mg. oral tablet of levofloxacin represents adequate prophylaxis for patients at low risk who undergo transrectal prostate biopsy. From April 2000 to May 2001 we prospectively evaluated 400 consecutive men who underwent transrectal needle biopsy of the prostate after a single 500 mg. oral dose of levofloxacin. Under an institutional review board approved protocol the drug was issued under a standing order by a clinic nurse 30 to 60 minutes before the procedure. Patients were issued 2 additional daily doses of levofloxacin if they were deemed at increased risk for infectious complications, that is if they had a large prostate more than 75 cc, diabetes mellitus, recent steroid use, severe voiding dysfunction or immune compromise. No patient received a cleansing enema before the procedure. Complications, the number of biopsy cores, prostate size and cancer detection rates were assessed. Only 1 of the 377 patients at low risk in whom biopsy was completed experienced a symptomatic urinary tract infection (0.27%). None of the 23 men at high risk who received additional doses of levofloxacin experienced a complication. Thus, the overall infection rate was 1 of 400 cases (0.25%) in this series. A mean of 7 biopsy cores (range 2 to 16) was obtained per patient and mean prostate volume was 49.75 cc (range 12 to 150). Prostate cancer was present in 93 patients (23%). A single 500 mg. dose of levofloxacin before transrectal needle biopsy of the prostate is effective and safe in patients at low risk. The administration of prophylaxis by a clinic nurse under a standing order optimizes patient compliance and physician efficiency. In patients at higher risk for infection additional antibiotic administration appears to provide adequate prophylaxis.