Background: Prognostic tools estimating survival of elderly patients with cerebral metastases from small-cell lung cancer (SCLC) improve treatment personalization. A specific tool for these patients was developed and compared to existing instruments. Methods: One-hundred-and-forty elderly patients (≥65 years) receiving whole-brain irradiation (WBI) for cerebral metastases from SCLC were retrospectively evaluated. WBI-program, age, gender, Karnofsky performance score, number of cerebral lesions, extracerebral metastases, and interval between SCLC-diagnosis and WBI were investigated. Characteristics significantly associated with survival in the multivariate analysis were used for the tool. Scoring points were calculated by dividing 6-month survival rates (%) by 10 and added for patient scores. The tool was compared to existing diagnosis-specific instruments including updated diagnosis-specific graded prognostic assessment (DS-GPA), Rades-SCLC and WBRT-30-SCLC. Results: In the multivariate analysis, KPS (P<0.001), number of cerebral lesions (P=0.013) and extracerebral metastases (P=0.049) were significantly associated with survival. Patient scores of 2 (n=37), 5 (n=69), 8 (n=20) and 11 (n=14) points were obtained; 6-month survival rates were 0%, 9%, 50% and 79% (P<0.001). The positive predictive value (PPV) of the worst group (2 points) to identify patients dying ≤6 months was 100%; PPVs of updated DS-GPA, Rades-SCLC and WBRT-30-SCLC were 94%, 100% and 94%. PPV of the best group (11 points) to identify patients surviving ≥6 months was 79%; PPVs of updated DS-GPA, Rades-SCLC and WBRT-30-SCLC were 86%, 79% and 100%. Conclusions: The most precise instruments were the new tool and Rades-SCLC for identification of patients dying ≤6 months, and the WBRT-30-SCLC to identify patients surviving ≥6 months.