This study sought to describe influenza vaccination coverages for different Spanish population subgroups, stressing the analysis of vaccination-related factors in subjects aged 50-64 years and estimating the possible beneficial effect of extending universal vaccination to this age group. A total of 6,400 surveys, targeting subjects over the age of 16 years and drawn from the 1997 Spanish National Health Survey, were used for study purposes. Influenza coverage was observed to rise significantly with age, and the reason cited by most subjects for seeking vaccination was medical indication. Coverage of the 50-64 age group was 21.6% (95% CI 19.4-23.8) and the variables associated with a greater probability of being vaccination were: residence in towns or cities with <10,000 inhabitants (OR 1.45); monthly income of less than 600 (OR 1.71); and presence of associated chronic disease (OR 3.07.) It is estimated that in Spain, 524,514 (40.7%) persons aged 50-64 years with associated chronic disease receive and 764,218 persons aged 50-64 years with associated chronic disease do not receive influenza vaccine. We conclude that the extremely high number of subjects in the 50-64 age range susceptible to influenza-related complications each year constitutes good grounds for universal vaccination being extended to said age group.