PURPOSE: The decision to attempt closed treatment on tibial shaft fractures can be challenging. At our institution, we attempt treatment of nearly all closed, isolated tibial shaft fractures. The purpose of this study was to report the results of 10 years of experience to develop a tool to identify patients for whom non-operative treatment of tibial shaft fractures may be a viable option. METHOD: This was a retrospective review of patients with tibial shaft fracture seen at a level 1 trauma center over 10 years. Patients with closed, isolated injuries underwent sedation, closed reduction, long-leg casting, and outpatient follow-up. Patients were converted to surgery for inability to obtain or maintain acceptable alignment or patient intolerance. Radiographic characteristics and patient demographics were extracted. Logistic regression analysis was used to develop a model to predict which patient and injury characteristics determined success of nonoperative treatment. RESULTS: 334 patients were identified with isolated, closed tibial shaft fractures, who were reduced and treated in a long leg cast. 234 patients (70%) converted to surgical treatment due to inability to maintain alignment, patient intolerance, and nonunion. In a regression model, coronal/sagittal translation, sagittal angulation, fracture morphology, and smoking status were shown to be significant predictors of success of nonoperative treatment (p < 0.05). We developed a Tibial Operative Outcome Likelihood (TOOL) score designed to help predict success or failure of closed treatment. The TOOL score can be used to identify a subsegment of patients with injuries amenable to closed treatment (38% of injuries) with a nonoperative success rate over 60%. CONCLUSION: Non-operative treatment of tibial shaft fractures is feasible, although there is a relatively high conversion rate to operative treatment. However, it is possible to use injury characteristics to identify a cohort of patients with a higher chance of success with closed treatment, which is potentially useful in a resource-constrained setting or for patients who wish to avoid surgery. LEVEL OF EVIDENCE: Prognostic Level 3.