BACKGROUNDS: The advent of penicillin has led to the marked reduction in the mortality from pneumococcal bacteremia, however, the mortality is still relatively high in this post-antibiotic era. Actually the prevalence of infection due to penicillin-resistant penumococci is increasing worldwide, and it is especially high in Korea due to irrelevant use of antibiotics. So, the high mortality of pneumococcal sepsis might be related to the emergence of penicillin-resistant strains, however, many other antibiotics, which eradicate pneumococci effectively, are available in these days. This has led us to suspect the role of penicillin- resistance in the high mortality rate. In this study, we evaluated the effect of penicillin resistance on the mortality of patients with penumococcal bacteremia. METHODS: The study population consisted of 50 adult patients with penumococcal bacteremia who were admitted between Jan, 1990 and July, 1997. Medical records were analyzed retrospectively. RESULTS: Most of the patients (96%) had underlying diseases. The most common local disease associated with pneumococcal bacteremia was pneumonia (42%), which was followed by spontaneous bacterial peritonitis (14%), cholangitis (10%), meningitis (8%), liver abscess (4%), pharyngotonsillitis (4%), sinusitis (2%) and cellulitis (2%). While the overall case-fatality rate in this study was 24%, it was higher when peumococcal bacteremia was associated with pneumonia (42%) or meningitis (50%). The rate of penicillin resistance was 40%, which was increased rapidly from 1991. The rate of penicillin resistance was significantly higher in patients with the history of recent antibiotics use and hospitalization within 3 months respectively. The clinical manifestations, that is, age, severity of underlying diseases, nosocomial infection, associated local diseases, and the presence of shock or acute renal failure were not statistically different between the patients with penicillin- resistant and -sensitive pneumococcal bacteremia. The mortality of patients infected with penicillin-resistant pneumococci was not statistically different from those with penicillin-sensitive pneumococcal bacteremia. CONCLUSION: Penicillin resistance is not associated with high mortality in adult patients with pneumococcal bacteremia. As the overall mortality is high, active penumococcal vaccination is recommended in patients with high risk of infection.