A telephone survey was conducted on 190 patients in Barcelona, Spain, at high-risk for influenza to evaluate the relationship between their knowledge and attitudes toward influenza and influenza immunization and whether they received the immunization. A discriminant function correlates (r = 0.86) with the immunization behavior and predicts the behavior before flu immunization in 84% of cases if we know the previous immunization behavior and adequately classifies the behavior in 82% if we don't know it (r = 0.75). Modifiable factors that predict immunization are self-identification as high-risk, belief that the immunization will not cause discomfort, intention to be immunized, and physician assigned. Those not immunized had a prevalent feeling that the shot is not effective, that they are not susceptible to the illness, and that the health center does not offer satisfactory organization to provide immunization. Furthermore, they felt that they had received controversial information through the mass media. We therefore believe that health education activities regarding influenza immunization should be specifically directed to increasing awareness of those who belong to a high-risk group, as well as to emphasizing susceptibility to the illness and the innocuousness of the immunization.