Objective. To describe the results of different measures implemented to improve adherence to the healthcare worker (HCW) influenza immunization program at BJC HealthCare during the period from 1997 through 2007. Design. Descriptive retrospective study. setting. BJC HealthCare, a 13-hospital nonprofit healthcare organization in the Midwest. Methods. We reviewed and analyzed HCW influenza vaccination data from all BJC HealthCare Occupational Health Services and hospitals during the period from 1997 through 2007. Occupational health staff, infection prevention personnel, and key influenza vaccination campaign leaders were also interviewed regarding implementation measures during the study years. Results. At the end of 2007, BJC HealthCare had approximately 26,000 employees. With the use of multiple progressive interventions, influenza vaccination rates among BJC employees increased from 45% in 1997 to 72% in 2007 (P < .001). The influenza vaccination rate in 2007 was significantly higher than in 2006: 72%, compared with 54% (P < .001). Five hospitals had influenza vaccination rates that exceeded the target goal of 80% in 2007. The most successful interventions were adding influenza vaccination rates to the quality scorecard incentive program and the use of declination statements, both of which were implemented in 2007. The most important barriers to success identified by interview respondents were HCWs' misconceptions about influenza vaccination and a perceived lack of leadership support. Conclusions. Influenza vaccination rates among HCWs significantly improved with multiple interventions over the years. However, the BJC HealthCare influenza vaccination target of 80% was not attained at all hospitals with these measures. More aggressive interventions, such as implementing mandatory influenza vaccination policies, are needed to achieve higher vaccination rates.