Since the mid-20th century, the role of health care in the lives of older Americans has increased exponentially. My dissertation project examines the ethical and epistemic uncertainties brought to the fore by expanding care to older patients. Each chapter of the dissertation centers a medical issue that prompted physicians and nurses to label the affected older patients as frail, gesturing at an imprecise yet culturally resonant notion of the distinctness of aging bodies. Tracing the drivers of therapeutic change for such conditions associated with frailty—namely, hip fracture, delirium, and incontinence—the project examines how understandings of aging bodies informed criteria of medical success, and the tolerance of poor outcomes. Ultimately, the project argues that history of care for frail older adults offers a critical lens into the nature of therapeutic change, the lived experience of disease in old age, and the role of health care in an aging society.