Abstract Background: Thoracoscopic diaphragmatic hernia (DH) repair has a high recurrence rate. Effective simulation modeling may improve technical performance for thoracoscopic DH repair. The study purpose was to evaluate measures of validity evidence for a low-cost thoracoscopic DH simulator. Materials and Methods: Synthetic diaphragm/intestine was connected to a to-scale left-sided neonatal rib cage and then covered with synthetic skin. Forty participants evaluated the DH repair simulator, using survey ratings that were analyzed for test content and internal structure validity evidence. Results: Observed averages (on a scale of 0-5) for the domains were 4.6 for Relevance, 4.5 for Value, 4.3 for Physical attributes, 4.0 for Realism of experience, 3.8 for Realism of materials, and 4.2 for Ability to perform. The highest observed averages were "relevance to practice" and "value, testing tool," whereas the lowest ratings were realism, intestines and realism, diaphragm. The observed average of global opinion ratings was 2.84/4.0, indicating the simulator can be considered for teaching thoracoscopic DH repair but could be improved. Experienced surgeons (more than eight DH repairs, at least four thoracoscopic repairs) had higher overall ratings than inexperienced surgeons (4.4 versus 4.1, P=.001). Conclusions: We successfully created a thoracic space relevant to a thoracoscopic DH repair and completed the model using inexpensive, readily accessible materials. After participants performed a simulated thoracoscopic DH repair, their ratings indicated the simulator was relevant to clinical practice and valuable as a learning tool but still requires improvements. Improvements and additional evaluation of validity evidence (content, internal structure, response processes, and relationship to other variables) are necessary prior to full implementation of this model as an educational tool.