Background: The majority of patients with gastrointestinal (GI) malignancies are older. Recently, it has become evident that elements from a geriatric assessment (GA) are powerful predictors of outcomes such as postoperative morbidity and mortality, length of stay, type of treatment received, and survival across several GI tumor types in older adults. A GA is a systematic evaluation of functional status, comorbidities, polypharmacy, cognition, nutritional status, emotional status, and social support. Methods: A PubMed search was performed in order to identify clinical studies investigating the association between GA and outcomes in patients with GI malignancies. Results: A total of 31 studies were included in this review. For colorectal cancer, the evidence linking GA variables and frailty to negative outcomes is substantial and consistent. The data regarding other GI malignancies is more limited, but generally shows the same findings. Conclusion: Increasing data shows that elements from a GA and frailty are consistently associated with negative short- and long-term treatment outcomes in older patients with GI malignancies. Future studies should investigate the impact of geriatric interventions on outcomes.