Aim: Repeated suicide attempts through intentional overdose are not infrequent, but little is known about the risk factors for intentional overdose. We aimed to investigate risk factors for the recurrence of intentional overdose within 1 year of discharge and to develop an index that predicts recurrence.Methods: This retrospective observational study included 419 patients admitted to our hospital between 2011 and 2018 because of an intentional overdose. Of them, 43 (10.0%) repeated an overdose within 1 year of discharge. The risk factors with the highest odds ratios in multivariate logistic regression analysis were used to develop an index Recurrence of Overdose Suicide Attempt. The predictive value of this index for recurrence was compared with that of the existing SAD PERSONS scale.Results: The following variables were significantly associated with recurrence and were included in the index: anxiety and/or insomnia at discharge; use of five or more psychotropic drugs; a neurotic, stress-related, or somatoform disorder; and female sex (odds ratios: 4.24; 5.52; 2.41; and 3.41, respectively). The newly developed index was a significantly better predictor of recurrence than the SAD PERSONS scale (area under the receiver operating characteristics curve, 0.797 vs. 0.668; p = 0.007). Sensitivity, specificity, and positive and negative predictive values for Recurrence of Overdose Suicide Attempt > 4 points (out of 6) were 72.1%, 75.8%, 25.4%, and 96.0%, respectively.Conclusion: The novel index can predict the recurrence of intentional overdose with a good negative predictive value and may therefore be a useful screening tool for this high-risk population.