OBJECTIVE: In spite of yearly recalls, influenza immunization rates of healthcare workers (HCWs) remained low (10%) at the University Hospitals of Geneva. This study was conducted to identify HCWs' reasons for rejection of immunization, to design specific intervention methods based on these reasons, and to evaluate the impact of such interventions. METHODS: Three departments with high-risk patients (geriatrics, obstetrics, and pediatrics) were selected as main targets. Questionnaires were distributed in these units. Based on HCWs' perceptions, different intervention methods were designed and used either in these departments only (educational conferences, on-site availability of a vaccination nurse) or in the whole institution (posters, personal letters). Immunization rates were collected throughout the institution. RESULTS: 797 completed questionnaires from 1,092 HCWs (73%) were returned. Major reasons for immunization rejection were confidence that their bodies' self-defense mechanisms would ward off infection (32%), perception of low exposure risk (23%), and doubts concerning vaccine efficacy (19%). The use of intervention methods designed to address these factors increased influenza immunization rates in the three targeted departments from 13% (95% confidence interval [CI95], 11.4-15.6) in 1995 and 1996 to 37% (CI95, 34.5-40.3) in the following season (P<.001). In all other departments, immunization rates rose from 9% (CI95, 8.5-10.3) to 23% (CI95, 21.6-24.1; P<.001). Nurses were, and remained, more reluctant to be immunized compared to other HCWs. CONCLUSIONS: Influenza immunization rates can be increased significantly by specific interventions based on local concerns of HCWs, among which educational conferences and the on-site availability of a vaccination nurse appeared important.