Purpose: Respiratory syncytial virus (RSV) is one of the most common causes of respiratory tract infections, especially in patients aged < 3 years. There are 2 antigenically different RSV subtypes, A and B. This study aimed to assess if the RSV subtype is independently associated with increased disease severity. Methods: We retrospectively collected data from the medical records of children hospitalized with RSV infection, aged < 3 years at Dong-A University Hospital between September, 2014 and December, 2018. Results: RSV A and RSV B infections were observed in 111 and 66 cases, respectively. Pneumonia was most commonly observed, followed by bronchiolitis in both subtypes. There were no significant differences between the groups regarding birth weight, gestational age, and incidence of having siblings. The duration of admission, duration of fever, and severity index were similar between the groups. The incidence of high fever (> 39°C) was slightly higher in the RSV B group (13.6%) than in the RSV A group (11.7%), although the difference was not statistically significant. Laboratory findings, including the neutrophil-lymphocyte ratio, were similar between the groups. The incidence of systemic steroid therapy was higher in the RSV A group (12.6%) than in the RSV B (3.0%) group (P= 0.03). Patients aged < 12 months, the incidences of oxygen therapy (P= 0.03) and systemic steroid therapy (P= 0.04) were higher in the RSV A group, suggesting that patients aged < 12 months with RSV A infection may have clinically more severe disease. Conclusion We recommend intensive monitoring if RSV A infection is detected in young children under 12 months.