Influenza is a common disease that is often perceived as self-limiting and mainly treated at home. However, for a portion of influenza suffers the disease may warrant a visit to the emergency room (ER) or hospitalization. OBJECTIVE: The purpose of this study is to estimate the resources consumed and associated costs of treating influenza patients in the ER and hospital. METHODS: Patient-level clinic and cost data were measured for the study population identified in the Premier Decision Support Services (DSS) databases. Data were analyzed retrospectively from January 1, 1997 to June 30, 1998 for patients with a diagnosis code for influenza using International Classification of Diseases, Ninth Revision-Clinical Modification (ICD-9) coding. Individual medication data were collected for a subset of the subjects in 1997 and all subjects in 1998. Data were summarized using means (±Standard Error) and multivariate analyses of variance (?=0.05) were performed to determine if observed differences in mean costs across demographic variables were statistically significant. RESULTS: Of the 1362 patients who met inclusion criteria, 333 (24.4%) required an inpatient hospital stay for influenza. The average total cost and charge per patient for ER only visits were approximately $142 and $218, respectively. The average total cost and charge per hospitalized patient were approximately $3251 and $5938, respectively. Other cost and demographic data are further detailed in the study. CONCLUSION: Influenza is not a benign disease. For some infected patients, ER or hospital care is needed. More aggressive and effective prevention and treatment strategies may lead to cost avoidance via fewer influenza related ER visits and hospitalizations.