Two patients with Bacteroides fragilis meningitis and ventriculitis were treated. In one infant infection developed at 2 1/2 months of age as a result of an infected ventriculoatrial shunt inserted to treat hydrocephalus. In the second patient ventriculitis and meningitis developed at 20 days of age, while he was convalescing from surgery for gastric perforation that had occurred at 5 days of age. Both patients were treated with ampicillin, chloramphenicol, and clindamycin, which sterilized the blood and lumbar cerebrospinal fluid but not the ventricular cerebrospinal fluid. The first patient received no further antibiotic therapy and died at 5 months of age. Metronidazole therapy sterilized the ventricular fluid of the second patient, who survived the infection. Ventriculitis should be suspected in patients with B fragilis meningitis. A brain scan should be done to detect signs of ventriculitis or brain abscess. Metronidazole may be the drug of choice in patients with B fragilis ventriculitis or meningitis who do not respond to chloramphenicol.