Influenza is a serious vaccine-preventable disease affecting 20% of the U.S. population each year. Vaccination of high-risk groups has been called the single most important influenza control measure by the Centers for Disease Control and Prevention. Studies show that vaccination can lead to decreases in flu-related illness and absenteeism among health care workers, as well as fewer acute care outbreaks and reduced patient mortality in long-term care settings. However, to date, voluntary programs have achieved only a 40% vaccination rate among health care workers, causing concern among government and infectious disease organizations. This article addresses the ethical justification for mandating influenza vaccination for health care workers. Health care workers' attitudes toward vaccination are presented, as well as historical and legal perspectives on compulsory measures. The ethical principles of effectiveness, beneficence, necessity, autonomy, justice, and transparency are discussed.