BACKGROUND: Emergence of pneumococcal resistance became a global issue since 1990s. According to the ANSORP studies with clinical isolates and carriage isolates between 1996 and 1999, some Asian countries showed alarmingly high prevalence of resistance to penicillin and other antimicrobial agents. To investigate the changing trends of pneumococcal resistance, ANSORP study group has performed a multinational surveillance study with invasive pneumococcal isolates from Asian countries. METHODS: All isolates from various invasive pneumococcal diseases were prospectively collected from 14 centers in 12 countries between November 1999 to August 2001. Broth microdilution tests with 16 antimicrobial agents were performed according to the NCCLS procedures. Serotyping was performed by means of Quelling reaction with use of group-specific antisera. RESULTS: A total of 685 isolates were collected. Overall, 52.4% of invasive isolates from Asian countries were not susceptible to penicillin (intermediate (I), 22.9%; Resistant (R), 29.5%). Vietnam showed the highest prevalence of penicillin non-susceptibility (I 20.6%, R 71.4%) followed by Sri Lanka (I 71.4%, R 14.3%), Hong Kong (I 24.1%, R 76%) and Korea (I 9.7%, R 54.8%). China (I 19.8%, R 23.4%) and Malaysia (I 9.1%, R 29.5%) also showed remarkable increase in penicillin resistance compared with previous ANSORP data, which were less than 10%. Vietnam (92.1%), Taiwan (87.7%), Korea (80.6%), and Hong Kong (76.8%) showed high prevalence of erythromycin resistance. MIC90s for ciprofloxacin were 4 microgram/mL (Hong Kong) and 2 microgram/mL (11 Asian countries except Hong Kong), respectively. CONCLUSION: Compared with previous data from ANSORP studies, antimicrobial resistance among invasive pneumococcal isolates has markedly increased in Vietnam, Sri Lanka, Taiwan, China, and Malaysia. Continuous surveillance of pneumococcal resistance in Asia is strongly warranted.