Background: Although Monteggia fracture dislocation is a rare injury, representing less than 1% of pediatric forearm fractures, missed Monteggia injuries are common, representing up to 50% of the acute injury. Both the acute and the chronic Monteggia injuries have different treatment protocols. There is a gray zone between the acute and the chronic Monteggia fracture dislocation, which represents the period after 2 weeks of injury until the ulnar fracture union. Objective: This study aimed to identify the treatment protocol for this gray zone between the acute and the chronic Monteggia fracture dislocation. Patients and Methods: Sixteen subacute Monteggia fracture dislocation patients (10 boys and 6 girls) underwent either closed or open reduction of the ulnar fracture with internal fixation. The patient's mean age was 9 years. Inclusion criteria conditioned a patient with Monteggia fracture dislocation after two weeks of the injury and before the ulnar fracture union. Results: By the end of the follow-up, all patients resumed full elbow range of motion with no elbow pain or deformity. All radiological parameters, including the radiocapitellar line and the ulnar bow lines, were normal at the end of the follow-up, with no redislocation of the radial head. Conclusions: Unlike the acute injury, there is no role for conservative treatment in the subacute Monteggia fracture dislocation. And contrary to chronic Monteggia, all patients didn't need open reduction of the radial head. Level of evidence: level IV.