Background: Anxiety and depression are associated with decreased quality of life, treatment adherence, and survival in patients with cancer. Mental Health Inventory (MHI-17) is a validated screening tool for psychological well-being, but cut points for older adults with cancer are unknown. The goal of this study is to identify cut points on MHI-17 Anxiety (MHI-A) and Depression (MHI-D) subscales which correlate with patient-reported anxiety and depression in older adults with cancer. Methods: This is a secondary analysis of baseline data from a randomized controlled trial in adults aged 65+ with solid tumors starting chemotherapy. At baseline, patients completed MHI-17. MHI-A and MHI-D were calculated (range 0-100; higher scores represent better mental health). Self-reported anxiety was obtained from single-item Linear Analog Scale Assessment (0-5 = low, 6-10 = high). Self-reported depression was obtained from Yale Depression Screen, “Do you often feel sad or depressed?” The association of MHI-A and MHI-D with the patient-reported outcomes was analyzed using logistic regression. Youden’s index was used to determine the optimal cut points for MHI-A and MHI-D for identifying patients with high anxiety and depression. Results: 458 patients (median age 71 (range 65-91), 57% female, 55% non-Hispanic white) were included in this analysis. The most common cancer types were: GI (31%), breast (19%), GU (18%), and pulmonary (16%); 75% had stage IV cancer. Twenty-four percent (N = 110) reported high anxiety and 21% (N = 97) depression. Median scores for MHI-A and MHI-D were 75 (range 0-100) and 80 (range 0-100). The optimal cut point for high anxiety on MHI-A was 65; this had an accuracy of 76.1%, a sensitivity of 71.8%, and a specificity of 77.5%. The optimal cut point for depression on MHI-D was 70; this had an accuracy of 80.1%, a sensitivity of 80.4%, and a specificity of 79.8%. Conclusions: The current study identified optimal cut points for MHI-Anxiety and MHI-Depression subscales to identify older adults with cancer starting chemotherapy with self-reported anxiety and depression. In the absence of patient-reported anxiety and depression, these cut points could be used to identify older patients with cancer at risk for poor mental health.