Pertussis outbreaks have been reported in various settings, including sports facilities, summer camps, schools, and health-care facilities. Mild and atypical manifestations of pertussis among infected persons and the lack of quick and accurate diagnostic tests can make pertussis outbreaks difficult to recognize and therefore difficult to control. Outbreaks among health-care workers (HCWs) are of special concern because of the risk for transmission to vulnerable patients. This report describes three pertussis outbreaks among HCWs and patients that occurred in hospitals in Kentucky, Pennsylvania, and Oregon in 2003. These outbreaks illustrate the importance of complying with measures to reduce nosocomial infection when evaluating or caring for patients with acute respiratory distress or cough illness of unknown etiology.