One hundred and eighteen (118) episodes of bacteremia and fungemia in children with cancer were compared to 401 episodes of bacteremia and fungemia in adults with cancer to assess differences in etiology, risk factors and outcome. A retrospective univariate analysis was performed of all episodes of bacteremia in national pediatric and adult cancer institutions appearing in 1990- 1996. A total of 519 episodes of bacteremia were assessed and compared. Both cancer centers differed in prophylactic antibiotic policies. About 50% of adults but less than 5% of children received quinolone prophylaxis during neutropenia, even though the empiric antibiotic therapeutic strategy was similar. There were differences in etiology between the groups: staphylococci and Stenotrophomonas maltophilia were more frequently observed in children (P<0.01), Pseudomonas aeruginosa and Acinetobacter spp. in adults (P<0.05). Gram-positive bacteremia was surprisingly more commonly observed in adults (65.7% vs 33.3%, P<0.01). Mixed polymicrobial bacteremia occurred more commonly in adults (31.8% vs 7.6%, P<0.001) than in children. Analysis of risk factors did not observe differences in risk factors except for underlying disease (acute leukemia was more frequently observed in children - 48.3% vs adults 33.7%, P<0.05 and prophylaxis: (prior prophylaxis with quinolones was more common in adults (47.5%) than in children (2.5%) P<0.0001). Overall and attributable mortality in pediatric bacteremia was significantly lower than in adults (P<0.03).