Background/Aims:To validate the AIMS65 score for predicting mortality of patients with nonvariceal upper gastrointestinal bleeding and to evaluate the effectiveness of urgent (<8 hours) endoscopic procedures in patients with high AIMS65 scores.Methods:This was a 5-year single-center, retrospective study. Nonvariceal, upper gastrointestinal bleeding was assessed by using the AIM65 and Rockall scores. Scores for mortality were assessed by calculating the area under the receiver-operating characteristic curve (AUROC). Patients with high AIMS65 scores (≥2) were allocated to either the urgent or non-urgent endoscopic procedure group. In-hospital mortality, success of endoscopic procedure, recurrence of bleeding, admission period, and dose of transfusion were compared between groups.Results:A total of 634 patients were analyzed. The AIMS65 score successfully predicted mortality (AUROC=0.943; 95% confidence interval [CI], 0.876 to 0.99) and was superior to the Rockall score (AUROC=0.856; 95% CI, 0.743 to 0.969) in predicting mortality. The group with high AIMS65 score included 200 patients. The urgent endoscopic procedure group had reduced hospitalization periods (p<0.05)Conclusions:AIMS65 score may be useful in predicting mortality in patients with nonvariceal upper gastrointestinal bleeding. Urgent endoscopic procedures in patients with high scores may be related to reduced hospitalization periods.