In France, the flu is responsible for thousands of deaths each year among vulnerable individuals. Flu vaccination is recommended for these individuals and for healthcare professionals who are at risk of transmitting the disease to patients. However, among hospital staff, flu vaccination coverage remains low, and the factors influencing vaccination uptake are poorly understood. A study was conducted at the Vichy and Montluçon hospitals to identify the determinants of influenza vaccination among staff. A case-control study was conducted at the two hospitals in Vichy and Montluçon in November 2004. Cases were randomly selected from among the salaried hospital staff at both hospitals who had received the influenza vaccination through occupational health services during the 2004–2005 vaccination campaign. Controls were randomly selected from among staff who had not received the vaccination. Cases and controls were interviewed face-to-face at their workplaces using a standardized questionnaire assessing knowledge and perceptions. Determinants of influenza vaccination were analyzed using multiple logistic regression. This approach was supplemented by focus groups conducted prior to the study with volunteer staff from both hospitals. A total of 402 staff members participated in the study: 144 cases and 258 controls. In multivariate analysis, influenza vaccination was significantly associated with having been vaccinated against influenza in 2002 and 2003 (OR=252, 95% CI: 74–850) or at least once in one’s lifetime (OR=11, 95% CI: 5–26), being aware of a vaccination campaign in the hospital (OR=26, 95% CI: 3–276), and feeling more at risk of catching the flu than other people (OR=4, 95% CI: 2–11). Vaccination was not associated with age, gender, or occupation. However, believing that the flu vaccine causes side effects and that alternative medicines are at least as effective as the vaccine were identified as barriers (OR=0.2, 95% CI: 0.1–0.5; OR=0.4, 95% CI: 0.2–0.9, respectively). These results are consistent with those found in studies conducted abroad. Focus groups help interpret the main factors: fear of side effects is strongly linked to the perception of hepatitis B vaccination, and the vaccine’s efficacy is often questioned. Conversely, personal or family vaccination habits are seen as encouraging vaccination. Future vaccination campaigns should address concerns about side effects associated with the flu vaccine. Furthermore, strong encouragement for staff who have never been vaccinated against the flu could lead to a first vaccination and help establish a regular vaccination schedule. (R.A.)