Influenza infections cause a substantial toll in respiratory infections, hospitalizations, and death; and immunization has proven effective in reducing these outcomes. This article describes a study to understand variations in influenza vaccination rates for a population ages 50 and older using data from a large insurer in Hawai'i. Vaccination rates were lower in adults without than with a chronic disease, and especially low in those without chronic disease of ages 50-64. People who had been vaccinated in the past year were likely to become vaccinated again, and people with a history of regular physician visits were more likely than others to become vaccinated. Having vaccine available at the worksite led to improved vaccination rates. By ethnicity Japanese, Koreans, and Chinese were most likely to obtain influenza vaccinations; the greatest ethnic differences occurred among adults ages 50 to 64 without a chronic disease. People seeing a physician during the influenza season were especially likely to become vaccinated during the week of the visit. Patients were more likely to become vaccinated by an existing physician than if seeing a new one. The percentage of office visits in weeks in which patients became vaccinated varied four-fold by physician specialty Internal medicine and family medicine physicians had the highest percentages whereas gynecologists and cardiologists had the lowest. The results suggest multiple reasons that high risk adults may fail to become vaccinated. Better understanding barriers may lead to improved strategies to improve influenza vaccination rates.