There is no standard tool for assessing the "functional age" of an older adult with cancer, although it is widely recognized that chronological age does not capture the heterogeneous physiological and functional status of older adults. Integrating a "geriatric assessment" into oncology research and clinical practice would help fill this void. Geriatric assessment covers factors that predict morbidity and mortality in older adults, including functional status, comorbidity, cognition, psychological state, nutritional status, and social support. This assessment provides a broader overall understanding of individual characteristics that affect life expectancy. In addition, this assessment identifies areas of vulnerability in older adults for which further evaluation or intervention is indicated. This article will address the utility of a geriatric assessment in oncology practice, review data that attest to the benefits of the assessment, and issue a call for further research into how this assessment can be integrated into oncology care. Doing so will help develop targeted interventions and optimize cancer outcomes in this rapidly growing population.