In April 2009, a novel influenza A(H1N1) virus was identified in Mexico and has since spread rapidly worldwide. The unique genetic and antigenic features of this virus have resulted in a high incidence of infection, with an epidemiologic profile that is different from that of previous seasonal influenza infections. As a consequence, a surge of pediatric patients has been presenting to emergency departments and physician's offices across the country during this 2009-2010 flu season. This article summarizes the clinical presentation of novel influenza A(H1N1) infection and identifies patient groups who are at high risk of severe disease. It also presents guidelines from the United States Centers for Disease Control and Prevention and the World Health Organization on diagnostic testing and management of patients with H1N1 infection, including postexposure prophylaxis and identification of patients who should be vaccinated.