The term "failure to thrive" is frequently used to describe older adults whose independence is declining. The term was exported from pediatrics in the 1970s and is used to describe older adults with various concurrent chronic diseases, functional impairments, or both. Despite this heterogeneity, failure to thrive has had its own international Classification of Diseases, Ninth Revision (ICD-9) code since 1979 and has been approached as a clinically meaningful diagnosis in many review articles. This conceptual framework, however, can create barriers to proper evaluation and management. The most worrisome of these barriers is the reinforcement of both fatalism and intellectual laziness, which need to be balanced with a deconstructionist approach, wherein the major areas of impairment are identified and quantified and have their interactions considered. Four syndromes known to be individually predictive of adverse outcomes in older adults are repeatedly cited as prevalent in patients with failure to thrive: impaired physical functioning, malnutrition, depression, and cognitive impairment. The differential diagnosis of contributors to each of these syndromes includes the other three syndromes, and multiple contributors often exist concurrently. Some of these contributors are unmodifiable, some are easily modifiable, and some are potentially modifiable but only with the use of resource-intensive strategies, initial interventions should be directed at easily remediable contributors in the hope of improving overall functional status, because a single contributor may simultaneously influence several other syndromes that conspire to create the phenotype of failure to thrive. How aggressively should more resource-intensive strategies for less easily modifiable contributors be pursued? This is a central clinical, ethical, and policy issue in geriatric medicine that cannot be settled without better process and outcome data. This paper examines the medical etymology of failure to thrive and proposes a rational approach to evaluation and management that is based on the limited medical literature.