the disease burden of respiratory syncytial virus (RSV) infection in the adult population has not been well characterized compared to children. investigation of the clinical characteristics and disease burden of adult RSV infection would help to establish public health policy and a future vaccine strategy. We retrospectively collected medical records of hospitalized adult patients who were diagnosed with RSV infection from January 2012 to December 2015 from three tertiary hospitals. Baseline characteristics, clinical outcomes and economic charge during hospitalization were compared by age groups (19-49 years, 50-64 years, and ≥ 65 years) using Chi-square test. The odds of risk factors of RSV pneumonia were calculated using binary logistic regression. A total of 204 patients from three hospitals were enrolled. Patients who older than 65 years were 132 (64.7%). 118 (57.8%) patients had clinically confirmed pneumonia and 22 (10.8%) died in a hospital. The median medical cost of RSV pneumonia was 2,855.26 USD (interquartile range, 1,561.85-5,379.55) per each admission. Solid cancer (adjusted OR, 3.85; 95% CI, 1.65-9.02, p = 0.002) and hematologic malignancy (all patients had pneumonia) were shown to be risk factors for RSV pneumonia. RSV infection in South Korea seemed to have a significant burden among adults as pneumonia, care in the intensive care unit and mortality. Nationwide awareness and further effort to recognize the current burden, prepare specific treatment, and prevent adult RSV infection would be necessary. Respiratory syncytial virus (RSV) belongs to the family of Paramyxoviridae and is the most important cause of lower respiratory tract infection in infants and young children. The virus causes common cold, bronchiolitis and pneumonia which are spread by close contact and large droplets. However, the clinical impact of RSV infection in adult populations had been underestimated until outbreaks in hospitals and healthcare facilities were identified. The infection may induce serious outcome especially in the elderly, patients with chronic cardiopulmonary disease and immunocompromised individuals 1. Also, the disease burden of RSV is not negligible compared to influenza among adults at high risk or the elderly 2,3. In the United States, annually 2-10% of community-dwelling older adults are infected and approximately 11,000 persons die due to the illness 4. In South Korea, RSV was detected in 1.1% of all adult respiratory infections and shows similar seasonal occurrence during childhood 5,6. Recently, the Strategic Advisory Group of Experts of the World Health Organization presented an issue of RSV vaccine production in April 2016, and stated that the elderly, pregnant women and immunocompromised patients would be the target populations of the RSV vaccine. Therefore, a precise investigation of the epidemiology and disease burden of adult RSV infection is key to establishing an accurate vaccine strategy. Furthermore, the increasing elderly population with debilitated host immune response and underlying comorb...