Background: Recognizing prognostic factors is important when evaluating elderly people with cancer to decide the appropriate treatment. The Oncogeriatric Index (OGI) was developed to predict early death (in 6 months) among elderly people with cancer, based on the Karnofsky Performance Status Scale, the Mini Nutritional Assessment and the Charlson Comorbidity Index. OBJECTIVES: To temporarily validate the OGI.Methods: We used a prospective cohort of cancer patients aged 60 or + years for GA n 605 (2015-2017) [training set]; 2016–2017: n 291 [validation set]) was performed during a six-month follow-up. Epidemiologic data and CGA (using 12 scales) before oncologic treatment were collected. The outcome was ED (within first 180 days). Cox’s proportional hazards model was used for the selection of prognostic factors. A prognostic score, the Onco Geriatric Index (OGI), was constituted of the number of abnormal CGA scales. Overall survival was estimated using the Kaplan–Meier method, and survival curves were compared using the log rank test. Predictive performance (calibration and discrimination) was determined. Results: There were 41 deaths among the 291 admitted patients. Patients who had three altered scales had 23.5 times higher risk of dying, adjusted for age, primary site of cancer and tumor staging (HR = 23.5, 95% CI 7.0-78.4, p < 0.001); those with two, 6.9 times (HR = 6.8, 95% CI 2.4-40.1, p < 0.001); and those with one, 3.1 fold (HR = 3.1, 95% CI 1.2-7.9, p = 0.020). The numbers of deaths predicted by the OGI were similar to those occurred, as well as a 6-month overlap of survival curves for each of the groups in the derivation and validation cohort, demonstrating that this prognostic model had an adequate predictive performance. Conclusions: Geriatric Index (OGI) is valid to evaluate elderly people with cancer in order to identify those at higher risk for early death.