Purpose: On average, adults aged 60 years or older have 2.2 chronic diseases, contributing to the over 60 million Americans with multiple morbidities. We aimed to understand the financial implications of the most frequent multiple morbidities among older adults. Design and Methods: We analyzed Health and Retirement Study data, determining out-of-pocket medical expenses from 1998 and 2002 separately and examining differences in the impact of multiple-morbidity constellations on these expenses. We paid particular attention to the most common disease constellations--hypertension, arthritis, and heart disease. Results: An increasing prevalence of multiple morbidity (58% compared with 70% of adults had two or more chronic conditions in 1998 and 2002, respectively) was accompanied by escalating out-of-pocket expenditures ($2,164 in 1998, increasing by 104% to $3,748 in 2002). Individuals with two, three, and four chronic conditions had health care expenditure increases of 41%, 85%, and 100%, respectively, over 4 years. Such patterns were particularly noticeable among the oldest old, those with higher educational attainment, and women, although having supplementary health insurance or Medicaid mitigated these expenses. Finally, there were significant differences in out-of-pocket expenditure levels among the multiple-morbidity combinations. Implications: Increasing rates of multiple morbidities in conjunction with escalating health care costs and stable or declining incomes among elders warrant creative attention from providers, researchers, and policy makers. Further understanding how specific multiple-morbidity constellations impact out-of-pocket spending moves us closer to effective interventions to support vulnerable elders. (Contains 7 tables.)