Thirty-eight cases of Gram-negative bacillary meningitis in adults have been identified over the past six years at the Veterans General Hospital, Taipei. Twenty cases were associated with head trauma and/or neurosurgery, while 18 cases occurred spontaneously. The overall mortality was 58%. Within the spontaneous meningitis group, 13 cases (72%) were due to Klebsiella pneumoniae, 11 cases (61%) were associated with bacteremia and eight cases (44%) with diabetes mellitus. In spite of the administration of third-generation cephalosporins, most cases of spontaneous meningitis (15 patients, 83%) died soon after diagnosis. In contrast, the clinical course for the postneurosurgical patients was more benign. Only seven patients (35%) died during the course of therapy. Common causative agents in postneurosurgical patients included Pseudomonas aeruginosa, Acinetobacter baumannii, and Escherichia coli. External cerebrospinal fluid drainage devices were thought to be the most important predisposing factor in Gram-negative bacillary meningitis in the postneurosurgical patients. Factors that adversely influenced the mortality of Gram-negative bacillary meningitis included the presence of bacteremia, shock, deep coma and a high initial cerebrospinal fluid leukocyte count.