Congestive heart failure (CHF) is a leading cause of hospitalization and mortality in the United States, affecting more than 5 million people at an expected cost of $34.8 billion in 2008. This article examines the association of medication adherence via the medication possession ratio with health care use and costs among Medicaid beneficiaries with CHF to estimate potential savings resulting from improved adherence. Using Medicare and Medicaid data for four states, researchers found that total health care costs were $5,910 (23 percent) less per year for adherent beneficiaries compared with nonadherent beneficiaries. Beneficiaries with adherence rates of 95 percent or higher had about 15 percent lower health care costs than those with adherence rates between 80 percent and less than 95 percent ($17,665 vs. $20,747), suggesting that the relationship between adherence and costs is graded. This study is the first to look beyond the 80 percent medication possession ratio threshold used in the relevant literature.