TO INVESTIGATE THE conditions that have developed in the treatment of posttraumatic meningitis with the use of new antibiotics, the authors studied cases with this infection retrospectively for a period of 68 months. Among 860 patients with moderate to severe head injuries, 12 (1.39%) sustained this complication. Of these, nine patients (75%) had a demonstrable basilar skull fracture and seven (58.3%) presented obvious rhinorrhea. Of these seven, four (57.1%) were treated conservatively and three (42.8%) finally underwent surgery for dural repair. The infecting agents were Gram-positive cocci (Staphylococcus haemolyticus,Staphylococcus warneri,Staphylococcus cohnii,Staphylococcus epidermidis, andStreptococcus pneumoniae) in five patients and Gram-negative bacilli in six patients (Escherichia coliin two,Klebsiella pneumoniaein two, andAcinetobacter anitratusin two). In one patient, the culture results were negative. All Gram-negative strains appeared resistant to ampicillin and third-generation cephalosporins, but sensitive to imipenem and to the quinolone ciprofloxacin. Gram-positive strains were sensitive to vancomycin. Hydrocephalus finally developed in the two patients who had received intrathecal infusions of amikacin. No other report of the relation of intrathecal infusion of antibiotics and the development of hydrocephalus was found. All patients survived, indicating that, for the present, posttraumatic meningitis is a nonfatal complication of head injury.