Indwelling urethral catheters are commonly used in patients admitted to acute care hospitals. Forty percent of nosocomial infections occur in the urinary tract, and greater than 80% of these infections are secondary to an indwelling urethral catheter. Fortunately, the majority of catheters are left indwelling for a short period of time. The duration of catheterization is directly related to the development of bacteriuria, nosocomial infection, and possible bacteremia with sepsis. A relatively low percentage of patients become infected during the first 3 to 5 days if sterile technique and proper maintenance of a closed system are performed. Bacteria may grow in the urine (planktonic) and ascend via the lumen, or bacteria in the biofilm around the outside of the catheter may infect the bladder. Most organisms are from the patient's intestinal flora, but exogenous sources on or near the patient may be involved. The major morbid events associated with the catheter are fever and the possible progression to bacteremia and sepsis. Early recognition of complications and arresting their progression, especially in the high-risk patient, are essential. Current research is directed at developing ways to reduce infection beyond the sterile closed system.