We studied for one year 60 patients separated in 3 groups of 20: first reference group without treatment; second group receiving netilmicin in premedication; third group treated by netilmicin for 2 days postoperatively. This series clearly demonstrates the high urinary tract infection rate after transurethral surgery, the benefit of antibioprophylaxis with netilmicin and the efficiency of one dose of this aminosid given one hour preoperatively.