To evaluate the clinical aspects of gram-negative bacillary meningitis (GNBM), we reviewed 41 adult patients with bacteriologically proven gram-negative bacillary meningitis, seen from 1985 to 1990. Thirty-two patients had post-neurosurgical GNBM and nine patients had spontaneous GNBM. Spontaneous GNBM appeared to have a sudden onset, a relatively fulminant course, and was caused most often by Escherichia coli. Post-neurosurgical GNBM, however, had a more insidious onset, a more protracted course, and was more often caused by nosocomial organisms which were resistant to multiple antibiotics. The overall mortality was 39%. Patients treated with combined aminoglycoside therapy had a lower mortality rate than those treated with intravenous aminoglycoside (17% vs 48%). The use of third-generation cephalosporins has made a significant therapeutic advance in the treatment of GNBM, with a lower mortality of 21%. We recommend treatment of GNBM with third-generation cephalosporins and aminoglycosides. If aminoglycosides are to be employed, it is suggested that they be administered both intravenously and directly into the central nervous system.