• Of 1,352 positive pediatric blood cultures during a 3.6-year period, two or more microorganisms grew from 72 cultures (5.3%), representing 60 patients. Based on predefined operational criteria for clinical interpretation of blood cultures, these cases were retrospectively classified as polymicrobial bacteremia (each organism, ie, a pathogen, 30%), mixed bacteremia/contaminant (20%), or multiple contaminants (50%). Considered individually, gram-positive organisms were isolated more frequently but were more often judged to be contaminants than the less common gram-negative organisms, which were more often thought to be true pathogens. Although one child did have a combined Streptococcus pneumoniae/Hemophilus influenzae bacteremia, these more common pediatric pathogens were underrepresented in those patients with polymicrobial bacteremia, from whom Enterobacterlaceae, streptococci, staphylococci, and anaerobes were more commonly Isolated. Hospitalization for a predisposing Illness and/or a focus of Infection occurred In 88% of the children with confirmed polymicrobial bacteremia.