The aim of this study was to determine how long it takes blood culture to become positive using a blood culture system that can be monitored continuously in pediatric patients. Data were collected prospectively on 1,000 positive blood culture results from a tertiary pediatric university hospital from April 2000 to May 2002. The laboratory used the BACTEC 9120 fluorescent blood culture system. Patient's age ranged from less than a day to 20 years of age (mean 3 years). Five hundred and four cultures (50.4%) out of 1,000 yielded coagulase negative staphylococcus (CNS), 81 (8.1%) S. aureus, 53 (5.3%). Pseudomonas and 50 (5.0%) Klebsiella species. Of the 504 coagulase negative staphylococcal blood culture isolates, 314 (62.3% of CNS) were regarded as skin contaminants. Of the 1,000 cultures, 9.6% were reported as positive in the first day, 27.8% in the second day, 54.7% in the third day, 77.0% in the fourth and 89.4% in the fifth day. There was no association between previous antibiotic usage and the period required for isolate recovery. The clinician can expect to get results of positive blood cultures with susceptibility data, at a rate of 77.1% by day four and almost 90% by day five of sampling in the bacteriemic patient. Blood cultures yielding coagulase negative staphylococci in the first three days almost always show bacteremia with those microorganisms.