Introduction: We report what is, to the best of our knowledge, the first case of pediatric trans-olecranon fracture dislocation of the elbow associated with a radial head fracture and with a medial collateral ligament disruption., Case Presentation: A 7-year-old girl presented to the emergency department after a fell on his right elbow while playful activity at home. The elbow X-ray showed acute trans-olecranon fracture dislocation of the elbow associated with a radial head fracture. A pre-operative 3D TC scans confirmed and clarified the injury pattern. However, stress radiographs performed in the operating room under anesthesia revealed an associated severe valgus instability caused by medial collateral ligament disruption. The olecranon fracture was fixed with two crossing 1.5 mm K-wires and the angulated radial neck fracture was fixed with a retrograde 1.5 mm K-wire by S.E.R.I. technique., Conclusion: Although trans-olecranon fracture dislocation of the elbow is well recognized and clearly described in adults, it is uncommon in children. A pre-operative 3D TC scans are recommended to enable a more accurate diagnosis and surgical planning. Medial collateral ligament has a central role in elbow stability and is very important to repair it during surgery., Competing Interests: None., (© 2021 The Authors.)