Background: Poor self-rated health (SRH) is a known predictor of mortality in the general adult population, but little is known about its use in older adults with cancer. The purpose of this study was to examine the association and ability of SRH to identify frail older adults and assess its ability to predict mortality in older adults with cancer. Methods: Using participants from the Cancer & Aging Resilience Evaluation (CARE) Registry who had undergone a geriatric assessment, we examined SRH using a single-item from the Patient-Reported Outcomes Measurement Information System (PROMIS) global health scale. SRH scores were dichotomized into Poor (poor and fair) and Good (good, very good, and excellent). Multivariable logistic regression analyses were used to examine associations between SRH and frailty (based on frailty index) and specific geriatric impairments adjusting for age, sex, comorbidity, cancer type and stage. Finally, the impact of SRH on all-cause mortality was assessed with a multivariable cox regression model. Results: A total of 708 participants with malignancy were included, median age was 68y, 41.5% male, and 74.6% White. Colorectal cancer was the most common cancer (27.1%) and 48.2% of the participants had Stage IV disease. Poor SRH was reported by 42% of participants and was associated with significantly higher odds of frailty (adjusted Odds Ratio [aOR] = 21.8; 95%CI 13.7-34.8). Similarly, poor SRH was independently associated with higher odds of impairments in Activities of Daily Living (ADL) (aOR = 5.6, 95%CI, 3.6-8.9), independent ADL (aOR = 8.4, 95%CI, 5.8-12.4), cognition (aOR = 4.6, 95%CI 2.3-9.3), malnutrition (aOR = 4.5, 95%CI 3.2-6.4), falls (aOR = 3.6, 95%CI 2.4-5.4), anxiety (aOR = 4.6, 95%CI 2.9-7.3), and depression (aOR = 5.4, 95%CI 3.0-9.7). The SRH demonstrated high sensitivity (84.3%) and specificity (78.4%) for identifying frailty, with a positive predictive value of 67% and negative predictive value of 90.6%. The 1y survival rate in those with Poor SRH was significantly worse (64.7% vs 84.3%, log rank p value < 0.001). In a multivariate cox regression analysis, poor SRH remained an independent predictor of worse survival (adjusted Hazard Ratio 2.29 [1.6-3.2], p< 0.01) after adjusting for age, sex, race, cancer type, stage, comorbidity, and planned treatment. Conclusions: Poor SRH is highly associated with frailty and could be a simple tool to identify frail older patients with cancer at risk for adverse events and increased mortality.