Objective: Anaerobic bacteremia rarely occurs in children. Therefore we assessed the usefulness of routinely obtaining anaerobic blood cultures in our pediatric patients. Study design: Records of 9360 paired aerobic and anaerobic blood culture bottles (Bactec NR660 System) containing blood specimens from pediatric inpatients and outpatients at Duke University Medical Center, Durham, N.C., were reviewed retrospectively. Yield and speed of detection were calculated for each bottle and compared for statistical significance by the McNemar test. Results: A total of 723 clinically important microorganisms were isolated; only 15 (2.1%) were strict anaerobes. Significantly more microorganisms (p <0.001), especially staphylococci, nonfermenting gram-negative rods, enteric gram-negative rods, and yeasts, were detected by use of the aerobic bottle. The anaerobic bottle was important in identifying an anaerobic microorganism as the cause of sepsis in only five patients, all of whom were at increased risk of having anaerobic infection. Conclusions: Anaerobic blood cultures are rarely helpful in the majority of pediatric patients and usually show positive results only in clinical settings associated with anaerobic infection. Microorganisms that prefer an aerobic environment, such as Pseudomonas aeruginosa and yeasts, are now far more common than anaerobes in children; aerobic culturing of the entire volume of blood collected might increase the yield from pediatric blood cultures. (J PEDIATR 1995;127:263-8).