Interpretation of blood cultures that are positive for coagulase-negative staphylococci (CoNS) is often difficult. Predictive values for blood cultures positive for CoNS in patients with a central vascular line in place were calculated using the following rates: true bacteremia, 3%; blood culture contamination, 2%; detection of bacteremia, 80%; and catheter colonization, 2% (for blood samples obtained through a central vascular line). Positive predictive values were 55% for 1 positive culture result of 1 culture performed, 20% for 1 positive result of 2 performed, and only 5% for 1 positive result of 3 performed. For 2 positive culture results of 2 cultures performed, the positive predictive value was 98% if both samples were obtained through the vein, 96% if one sample was obtained through a catheter and the other was obtained by vein, and only 50% if both samples were obtained through a catheter. Use of this model with institution-specific values for input parameters would assist in clinical decision-making as well as hospital quality assurance.