Between January 1986 and December 1999, 109 adult patients with culture-proven community-acquired bacterial meningitis were identified at Kaohsiung Chang Gung Memorial Hospital. To compare changes over time, the appearance of disease among our patients was divided into two equal time periods: an earlier time period (1986-1992) and a later time period (1993-1999). In this study, there was a decreasing proportion of community-acquired bacterial meningitis compared with nosocomial bacterial meningitis in adult patients in recent years. Its proportion declined dramatically from 81% in the earlier 7 years to 37% in the later 7 years. Of the pathogens, Klebsiella (K.) pneumoniae was the most frequently implicated pathogen, followed by Viridans (V.) streptococci, Streptococcus pneumoniae, and Staphylococcus aureus. Other rare organisms including Acinetobacter baumannii, Salmonella Group B and D, Proteus mirabilis, Group B, D, and non-A, non-B and non-D streptococci, and coagulase-negative staphylococci emerged during the second period. There was a decrease in the mortality rate from 44% in the first to 34% in the second time period, but the overall mortality rate remained high. Of the implicated pathogens, patients infected with V. streptococci had a consistently favorable prognosis, while a dramatic decrease in the mortality rate of those infected with K. pneumoniae was seen in recent years. In the multiple logistic regression analysis, only the presence of septic shock and seizures was independently associated with mortality. The timing of appropriate antimicrobial therapy, as defined by consciousness level, was a major determinant of survival and neurological outcomes for patients with community-acquired bacterial meningitis, and the first dose of an appropriate antibiotic should be administrated before a patient's consciousness deteriorates to a Glasgow coma scale score lower than 10.