An apparent increase in the incidence of enterococcal bacteremias from 7 to 48/1000 bacteremias during 1986 to 1991 (p < 0.01) prompted this descriptive clinical and molecular epidemiologic study of 83 episodes occurring in 80 children between 1986 and 1992. Most community-acquired cases were in infants, in comparison with nosocomial episodes (24/26 and 34/57; p < 0.01); many of them were neonates (10/26 and 6/57; p < 0.01). Nosocomial cases were associated with underlying conditions including major surgery 56%, immunosuppression 49%, organ and tissue transplants 30%, and cardiac 32%, pulmonary 25%, renal 21%, and hepatic 21% disorders. Nosocomial episodes developed after a median of 32 days. There were 58 primary and 25 secondary bacteremias. Thirty-two episodes were polymicrobial and 44 organisms were involved. Twenty-six percent of the patients died. In 15%, death was preceded by septic shock, disseminated intravascular coagulation, and polymicrobial bacteremia (p < 0.01). Of 75 isolates, 82% were Enterococcus faecalis and 14% were Enterococcus faecium. Fourteen E. faecalis strains produced hemolysin; none produced beta-lactamase. Three had high-level resistance to gentamicin and 13 to streptomycin; two E. faecium and none of the E. faecalis strains were vancomycin resistant at a low level (p < 0.01) and one was ampicillin resistant. Pulsed-field gel electrophoresis of whole-cell DNA digested with restriction enzymes Sma I and Eag I showed five isolates with a homogeneous pattern, two with another homogeneous pattern, and 68 with distinct heterogeneous patterns. The increase in enterococcal bacteremias was not due to a clonal strain dissemination but to an increase in cases of heterogeneous enterococcal strains. We conclude that enterococcal septicemia is now an important cause of serious morbidity and death in critically ill children.