In elderly patients, failure to thrive describes a state of decline that is multifactorial and may be caused by chronic concurrent diseases and functional impairments. Manifestations of this condition include weight loss, decreased appetite, poor nutrition, and inactivity. Four syndromes are prevalent and predictive of adverse outcomes in patients with failure to thrive: impaired physical function, malnutrition, depression, and cognitive impairment. Initial assessments should include information on physical and psychologic health, functional ability, socioenvironmental factors, and nutrition. Laboratory and radiologic evaluations initially are limited to a complete blood count, chemistry panel, thyroid-stimulating hormone level, urinalysis, and other studies that are appropriate for an individual patient. A medication review should ensure that side effects or drug interactions are not a contributing factor to failure to thrive. The impact of existing chronic diseases should be assessed. Interventions should be directed toward easily treatable causes of failure to thrive, with the goal of maintaining or improving overall functional status. Physicians should recognize the diagnosis of failure to thrive as a key decision point in the care of an elderly person. The diagnosis should prompt discussion of end-of-life care options to prevent needless interventions that may prolong suffering.