In an eight year period (1972-1979), 158 cases of enteric gram-negative bacillary meningitis and 53 cases of Listeria meningitis were reported to the New York City Health Department. These two forms of bacterial meningitis were the fourth and fifth most common ones reported to the Department, respectively. The cumulative total of reported cases of gram-negative rod meningitis over this less than the reported cases due to Neisseria meningitis over this period. In contrast to most previous studies of Listeria and enteric gram-negative meningitides, the majority of cases occurred in adults. Listeria meningitis occurred more often in immunosuppressed hosts and the elderly than in the newborn; gram-negative bacillary meningitides were seen more often in elderly septic patients and in patients with traumatic skull fracture than in infants during the first months of life. The over-all mortality of Listeria meningitis was 62 percent; that of the combined gram-negative meningitides 71.3 percent. The mortality in adults with Escherichia coli and Klebsiella meningitis who were treated with chloramphenicol as the major antibiotic was 83 percent. In comparison, the only appreciable survival rates noted were in those with Listeria, Escherichia coli, Proteus mirabilis and Salmonella meningitis who were treated with ampicillin alone in whom the over-all mortality was 51 percent.