Nosocomial urinary tract infection (UTI) is the most common infection acquired in both hospitals and nursing homes and is usually associated with catheterization. This infection would be even more common but for the use of the closed catheter system. Most modifications have not improved on the closed catheter itself. Even with meticulous care, this system will not prevent bacteriuria. After bacteriuria develops, the ability to limit its complications is minimal. Once a catheter is put in place, the clinician must keep two concepts in mind: keep the catheter system closed in order to postpone the onset of bacteriuria, and remove the catheter as soon as possible. If the catheter can be removed before bacteriuria develops, postponement becomes prevention.