The estimated average economic cost of influenza in the United States exceeds $1 billion each year, and the actual cost is more likely on the order of $3 to $5 billion per year. Benefit-cost models generally indicate that the benefits of influenza immunization for persons aged 65 and over outweigh the cost (when one excludes the cost of medical care in the additional years of healthy life gained by immunization). The low acceptance of influenza immunization suggests that individuals do not see the benefit-cost equation in the same way that policymakers do. This article presents a benefit-cost equation from an individual's perspective. The model demonstrates that pre-season immunization is cost-effective when the cost of a case of influenza, were it to occur, would be very high--as it is in persons under active medical care for heart or lung disease, for example. Immunization is also cost-effective for persons with a high income and a low cost of immunization--such as physicians themselves. The model further demonstrates that in the face of an actual epidemic, one can justify greater expenditures on protection against influenza, including immunization plus chemoprophylaxis or early chemotherapy. Finally, analysis of the model suggests the need for improved, less expensive systems for protecting individuals against influenza.