The deleterious effects that debt can have on health outcomes are well documented, yet comprehensive studies of the debt-health link for older adults remain limited even as their indebtedness has increased dramatically in recent decades. Additionally, the literature cannot explain the causal pathway linking poor health with debt. Using data from the Health and Retirement Study (1998–2016), we examine a range of physical and mental health measures and assess how they may be shaped by the amount and type of debt held by older adults. To address the likely endogeneity of debt and health, we employ marginal structural models, developed specifically as an identification strategy in the presence of possible endogeneity, alongside population-averaged models that allow us to compare outcomes for populations with and without debt without relying on unverifiable assumptions regarding the underlying population distribution as is the case with random- and fixed-effects models. Findings indicate that carrying any debt has a negative effect on a range of health outcomes for older adults, including objective and subjective physical and mental health. In addition, the more debt older adults carry, the more detrimental it is for their health. Finally, the type of debt matters: while secured debt has a limited, if any, negative impact on health outcomes, unsecured debt has a substantial negative impact on health. Policymakers should design policies that promote the prudent use of debt and discourage carrying large debt burdens, especially unsecured debt, into retirement as this would promote better health outcomes for older Americans.