The semiquantitative culture technique is a standard procedure for the laboratory diagnosis of catheter-associated infections and catheter-associated bacteremia. In a prospective observational study, we evaluated the clinical impact of the semiquantitative culture results on the treatment of the patient. Clinical impact was defined as a change in diagnosis or therapy on the basis of the semiquantitative culture result. One hundred fifty-seven catheters consecutively submitted from the surgical intensive care unit to the laboratory were studied. In 96% of the episodes, no clinical impact was observed. In the other 4%, clinical decisions were guided mainly by the concurrent positive blood cultures. Newer laboratory techniques that do not require removal of the catheter are needed to guide therapeutic decisions.