Introduction: Gastrointestinal bleeding is a frequent cause of hospital admissions in older adults with relatively high mortality. Comprehensive geriatric assessment (CGA) is a multidimensional tool for adequately evaluating the elderly. Our study aimed to evaluate the usefulness of the CGA, including the multidimensional prognostic index (MPI), in elderly patients hospitalized for acute upper gastrointestinal bleeding (AUGIB). Moreover, our study aimed to identify the possible risk factors for unfavorable outcomes and mortality. Methods: This study was designed to analyze data from elderly patients aged ≥65 years with AUGIB. They were followed for one month. Results: The study included 166 patients aged ≥65 years, 90 males and 76 females; their ages ranged from 65-91 with a mean ± SD of 72.7 ± 6.5. In descending order, the most common endoscopic causes of AUGIB were esophageal varices (35.5%), peptic ulcer (27.1), erosive gastritis (9.6%), esophageal ulcer (7.8%), antral gastritis (5.4%), gastric mass (3.6%), post band ulcer (2.4%), and angiodysplasia (1.2%). Furthermore, the results revealed a statistically significant difference between the mortality and Rockall scores, with a P-value of 0.002. Besides, the data showed a strong correlation between the incidence of mortality and CGA with a P-value of < 0.001. Our study showed a strong positive correlation between MPI, Blatchford score, Rockall score, and days of hospital stay. Moreover, it revealed a strong relation between MPI and mortality (P-value <0.001). Conclusion: A comprehensive geriatric assessment of the elderly with a calculation of MPI can predict the outcome of upper gastrointestinal bleeding.