BACKGROUND: The unabated rise in medication costs particularly affects older persons with chronic conditions that require long-term medication use, but how prescription benefits affect medication adherence for such persons has received limited study. OBJECTIVE: We sought to study the relationship among prescription benefit status, health, and medication acquisition in a sample of elderly HMO enrollees with 1 or more common, chronic conditions. RESEARCH DESIGN: We implemented a cross-sectional cohort study using primary survey data collected in 2000 and administrative data from the previous 2 years. SUBJECTS: Subjects were aged 67 years of age and older, continuously enrolled in a Medicare + Choice program for at least 2 years, and diagnosed with 1 or more of hypertension, diabetes, congestive heart failure, and coronary artery disease (n = 3073). MEASURES: Outcomes were the mean daily number of essential therapeutic drug classes and refill adherence. RESULTS: In multivariate models, persons without a prescription benefit acquired medications in 0.15 fewer therapeutic classes daily and experienced lower refill adherence (approximately 7 fewer days of necessary medications during the course of 2 years) than those with a prescription benefit. A significant interaction revealed that, among those without a benefit, persons in poor health acquired medications in 0.73 more therapeutic classes daily than persons in excellent health; health status did not significantly influence medication acquisition for those with a benefit. CONCLUSIONS: Coverage of prescription drugs is important for improving access to essential medications for persons with the studied chronic conditions. A Medicare drug benefit that provides unimpeded access to medications needed to treat such conditions may improve medication acquisition and, ultimately, health.