Approval for this study was obtained from the institutional review boards of the University of Utah and Primary Children's Medical Center. We conducted a retrospective study of children hospitalized with 2009 H1N1 influenza infection and neurological complications between April 1, 2009 and November 30, 2009. Patients were included if they were <19 years old at the time of presentation, were hospitalized with confirmed pandemic 2009 H1N1 influenza virus, and had a neurological complication that led to or complicated the hospitalization (and was not secondary to some systemic problem causing a neurological complication). Neurological complications included seizures, febrile seizures, status epilepticus, encephalopathy, encephalitis, myositis, myalgia, aphasia, ataxia, neuropathy, Gullain-Barre syndrome, or other focal neurological complaints. We used children hospitalized with seasonal influenza and neurological complications as a comparison group, for the time period July 1, 2004 through June 30, 2008. The study was conducted at a children's hospital that provides both primary and tertiary care services. The cachement area has an estimated pediatric population of >1 million children distributed among Utah, Idaho, Wyoming, Nevada, and Montana.5 First and second wave activity was defined as April 1 to July 31 and August 1 to November 30, 2009. These ranges for each pandemic wave were based on the incidences of new H1N1 influenza admissions at our institution. We searched records of children known to the neurology service directly, as well as using a computer-based screen of all patients identified with laboratory-confirmed influenza A together with at least 1 of the International Classification of Diseases, Ninth Revision, Clinical Modification codes for a neurological diagnosis (see Supporting Information Methods). The positive predictive value of direct fluorescent antibody (DFA) staining for influenza ranged from 85 to 100%6 and is monitored annually.