BACKGROUND: Older adults comprise the majority of patients with gastrointestinal (GI) cancer. Geriatric assessments (GAs) are recommended for older adults with cancer in part to detect aging-related impairments (e.g., frailty) associated with early mortality. Social factors like social vulnerability may also influence aging-related impairments. However, the association between social vulnerability and aging outcomes among older adults with cancer is understudied. METHODS: The authors included 908 older adults aged 60 years and older who were recently diagnosed with GI cancer undergoing GA at their first prechemotherapy visit to the University of Alabama at Birmingham oncology clinic. The primary exposure of interest was the social vulnerability index (SVI). Outcomes were frailty (frail vs. robust/prefrail) and total number of GA impairments (range, 0-13). The authors examined the association between SVI and outcomes using Poisson regression with robust variance estimation and generalized estimating equations. RESULTS: The median age at GA was 69 years (interquartile range, 64-75 years), 58.2% of patients were male, 22.6% were non-Hispanic Black, 29.1% had colorectal cancer, 28.2% had pancreatic cancer, and 70.3% had stage III/IV disease. Adjusting for age, sex, cancer type, and disease stage, each decile increase in the SVI was associated with an 8% higher prevalence of frailty (prevalence ratio, 1.08; 95% confidence interval, 1.05-1.11) and a 4% higher average count of total GA impairments (risk ratio, 1.04; 95% confidence interval, 1.02-1.06). The results were attenuated after further adjustment for race and education. CONCLUSIONS: Greater social vulnerability was associated with a higher prevalence of frailty and an increasing average number of GA impairments among older adults with GI cancers before systemic treatment. Intervening on social vulnerability may be a target for improving the risk of frailty and GA impairments, but associations of race and education should be further evaluated.