BACKGROUND: Streptococcus pneumoniae is one of the most important causes of pneumonia, meningitis, bacteremia, and other invasive diseases in children and adults. The 23-valent polysaccharide pneumococcal vaccine (PPV) has been recommended to adults with high risk conditions by the Korea Society of Infectious Diseases in 2007, but there is no data on the epidemiology of invasive pneumococcal disease in Korean adults to support this recommendation. Therefore, we performed a study to investigate the epidemiology of invasive pneumococcal disease in Korean population. MATERIALS AND METHODS: We collected clinical and microbiologic data of patients diagnosed with invasive pneumococcal disease (IPD) in 3 university-hospitals located in Seoul and Gyeonggi-do from January 2002 to December 2007. RESULTS: A total of 168 patients were diagnosed with IPD in the selected hospitals during the study period. Invasive pneumonia and meningitis were the most common forms of IPDs. The mean length of hospitalization of patients with IPD was 18.5+/-26.7 days and mortality rate of IPD was 18.6%. Among the isolates from patients with IPD, 59.7% was susceptible to penicillin and 38.3% was susceptible to erythromycin. Mortality rate of IPD increased with age and in patients with Eastern Cooperative Oncology Group performance status 4. CONCLUSIONS: Epidemiology of IPD in Korean population was described. Further studies should be performed to secure the risk factors of invasive pneumococcal diseases and to confirm the appropriateness of recommendation for vaccination with the 23-valent PPV.