The bacteriology and clinical findings of ten pediatric patients with lung abscess are presented. Bacteriologic data were based on percutaneous transtracheal aspiration obtained before initiation of antimicrobial therapy. Anaerobic bacteria were present in all ten patients; in nine they were mixed with aerobic bacteria. The most frequent isolates were Peptostreptococcus (8), Peptococcus (5), Bacteroides melaninogenicus (6), and Bacteroides fragilis (3). The aerobic isolates most frequently recovered were alpha-hemolytic streptococci (5), group A beta-hemolytic streptococci (4), and Escherichia coli and Klebsiella pneumoniae (4 each). Virtually all abscesses were located in dependent pulmonary segments. Antimicrobial therapy was guided by the bacteriologic findings and was successful in all instances.