In order to determine the species responsible for viridans-group streptococcal meningitis in adults in Taiwan, seven cases of culture-proven meningitis due to these organisms were studied. The cases were all identified at the Chang Gung Memorial Hospital-Kaohsiung over a period of 3 years, and they accounted for 9% (7/78) of all cases of culture-proven bacterial meningitis occurring in adults during this period. Of the seven viridans streptococci isolates recovered, Streptococcus constellatus accounted for four, Streptococcus anginosus for two, and Streptococcus oralis for one. Thus, it appears that streptococci of the milleri group are the most common species causing bacterial meningitis in adults in Taiwan. The tendency for these organisms to cause invasive central nervous system infections in adults should not be overlooked when these species are recovered from cerebrospinal fluid specimens.