Uncertainty regarding the benefits of influenza vaccination may contribute to the underutilization of this vaccine. We have conducted serial cohort studies using the administrative data bases of a Twin Cities based managed care organization to assess the impact of disease and benefits of vaccination among the elderly. For the 6 seasons 1990-1991 through 1995- 1996, there were more than 20,000 elderly members of the health plan included in each cohort. Data collected included information on baseline demographic and health characteristics, vaccination status and outcomes (hospitalizations and death). Multivariate regression techniques were used to compare the risks of outcomes between vaccinated and unvaccinated persons while controlling for covariates and confounders. Results for data pooled over the 6 seasons demonstrated that influenza vaccination was associated with significant reductions in hospitalizations, outpatient visits, and death among the elderly. Similar findings were observed for low, intermediate, and high risk subgroups. Vaccination was also associated with cost savings. These findings are consistent with results from studies conducted in other countries and over other seasons and strongly support age-based recommendations for annual influenza vaccination for all persons ages 65 and over.