Background: Pediatric patients in treatment for cancer can have fatal bacterial infections. Thus, in the presence of fever or other signs infection, antimicrobials have to be prescribed empirically. Aim: To know the causative agents of bacteremia in children with cancer, their changes with time and between different hospitals and their patterns of susceptibility. Material and methods: We reviewed the blood cultores of children with cancer in five hospitals of Santiago, from 1994 at 1998. Results: During the study period, 707 agents were isolated. The most frequently isolated species or genus were coagulase negative Staphylococcus (43%), Staphylococcus aureus (16%), Escherichia coli (9%), Klebsiella spp. (8%), Pseudomonas spp. (5%) and Candida spp. (4%). Coagulase negative Staphylococcus was 55% resistant to meticilin and S. aureus was 44% resistant. Enterobacteriae had 15% resistance to gentamicin and amikacin, 2% to imipenem, 26% to ceftriaxone, 21% to cefotaxim and 20% to ceftazidim. Among non fermenting agents resistance was 6% for imipenem, 9% for amikacin 10% for ciprofloxacin, 19% for ceftazidim and 22% for cefoperazone. The resistance of Streptococcus spp. (non pneumoniae) to penicillin reached 50% and that of Enterococcus spp. was of 33%. Conclusions: Treatment for pediatric patients with cancer must be modified and new guidelines including more active medications for patients at risk for bacteremia, should be devised (Rev Méd Chile 2001; 129: 1297-1304)