Using a randomized, retrospective case control survey approach, this study compared employees immunized (cases) to a group of non immunized employees (controls) between the months of October and December 1994. In May 1995, a self administered questionnaire was distributed to employees working at the Hanford nuclear reservation located in eastern Washington State. Bivariate analysis included chi-square tests to study the association between influenza vaccine and rates of influenza like illness and related complications, rates of employee absenteeism, rates of physician visits, use of prescribed medication, and rates of hospitalization. To assess the economic benefits associated with vaccination, analysis included estimating the direct and indirect costs associated with immunization and influenza like illnesses, and complications related to influenza like illnesses. Responses to the survey resulted in 789 employees in the vaccinated group and 931 employees in the nonvaccinated group. As compared to vaccinated employees, nonvaccinated employees reported significantly higher rates of episodes of influenza like illness (78 per 100 compared to 59 per 100, p < 0), influenza related complications (8.0 compared to 5.0, p < .01), lost work days (63 per 100 compared to 35 per 100, p < 0), use of prescription medication (18.6 per 100 compared to 8.7 per 100, p < 0), physician visits (18.6 per 100 compared to 8.7 per 100, p < 0), and inpatient hospital. Cost savings were estimated to be $83.84 per person vaccinated. The results of this study suggest this worksite influenza vaccination program produced significant health related and economic benefit to employee participants and their employers.