To evaluate and compare the epidemiological patterns and clinical courses of influenza A and B among children and adults, we retrospectively reviewed the medical records of 809 children and 271 adolescents/adults with laboratory-confirmed influenza between October 2011 and May 2012 at a tertiary-care Hospital. Children with influenza B presented with a high fever (body temperature > 39℃), sputum production, diarrhea, nausea/vomiting, and myalgia more frequently than those with influenza A. Children with influenza B also showed longer intervals from symptom onset to initiation of antivirals and higher antibiotic prescription and hospitalization rates than those with influenza A. Adults aged 20-59 years accounted for approximately 16% and 20% of the patients with influenza A and those with influenza B, respectively. Though the clinical manifestations and outcomes were similar between adult patients with influenza A and those with influenza B, influenza B may cause substantial disease burden among not only children but in socially active adults aged 20-59 years.