Clinical signs are not sufficiently reliable for establishing diagnosis of intravascular catheter-related infection. Therefore, microbiological confirmation, based on the culture of the catheter tip after its removal, is necessary in diagnosing the infection. The aim of this study was to determine the frequency and the degree of microbial colonization of intravascular catheters (IVK), and the risk for the onset of sepsis, by using qualitative, semiquantitative (roll plate) and quantitative (vortexing) catheter culture techniques. During the period April 2001-December 2002, 289 intravascular catheters were cultured. A total of 284 microorganisms were isolated from 217 (75%) culture-positive catheters. The frequency of isolation of some organisms was the following: coagulase-negative staphylococci (CNS) 41%, Staphylococcus aureus 19%, Enterococci spp 6%, other gram-positive microorganisms 9%, gram-negative microorganisms 21%, and fungi 4%. In 35 catheters, cultures were polymicrobial; two microorganisms were found in 25 cultures and three were found to be in 10 cultures. There were 122 (46%) intravascular catheters, which were found significantly colonized. A high rate of positivity and a high rate of S. aureus isolates and gram-negative bacteria indicate the need of establishing the exact microbiological diagnosis of these infections, and the rigorous undertaking of adequate control and preventive measures.