The present study aimed to test the validity and reliability of the Geriatrics 8 (G8) tool, a risk-screening tool for further comprehensive geriatric assessment, with hematologic cancer patients aged 65 years and older. METHODS This methodological study included 110 patients followed up for hematologic cancer. Data were collected using the patient identification form, the G8 screening tool, and the Edmonton Frail Scale. Language and content validity, internal consistency, confirmatory factor, sensitivity and specificity and concurrent validity analyses were also used. RESULTS Patients (mean age: 73.9±6.10) were diagnosed with lymphoma (30.9%), multiple myeloma (21.8%), leukemia (20.9%), myelodysplastic syndrome (19.1%). Confirmatory factor model fit index analysis χ²/ df and p-values (0.14) showed a good fit and GFI, AGFI, SRMR, and RMSEA values showed acceptable fit. The Cronbach's alpha coefficient was 0.655, area under the ROC curve was 0.824 (95%, 0.745-0.904), and sensitivity and specificity were 61.0% and 88.9%, respectively. CONCLUSION The findings indicated that the G8 screening tool was found a valid and reliable tool for geriatric patients diagnosed with cancer to determine the risk and need for further comprehensive geriatric assessment.