Older patients often suffer from multiple co-morbid conditions. Few co-morbidity indices are valid and reliable in elderly patients and comparison between them is rare. Our objective was to compare the performance, relevance, and abilities of six widely used and validated co-morbidity indices--the Charlson Cumulative Illness Rating Scale-Geriatrics (CIRS), Index of Co-Existent Disease, Kaplan Scale, Geriatrics Index of Co-morbidity (GIC), and Chronic Disease Score--to predict 5 years of survival after hospital discharge. Data came from a prospective study with yearly follow up, conducted 2004-2009 in 444 patients (mean age 85 years; 74% female) discharged from the acute geriatric hospital of the Geneva University Hospitals. In univariate analysis, mortality was significantly associated with age; each supplementary year added 7% of additional risk; and with sex, being male increased the risk by 1.5-fold. The best prognostic predictor was the GIC class 4 followed by the CIRS quartile 4 multiplying the risk of death by 4 and 3, respectively. After 1 year of discharge, for both scores approximately 50% of the high-score patients were already deceased and 80% were deceased after 5 years, compared with <5% in the lowest scores after 1 year and <40% after 5 years. When we entered all of the significant independent variables in a stepwise backward analysis, the best multiple regression model retained the CIRS quartile 4 as the strongest risk predictor followed by the GIC class 4. We conclude that the CIRS and the GIC may improve hospital discharge planning as being useful for clinical decision-making purposes and for clinical research in older patients.